What about Attributes?
If you are a Stamina based damage dealer they all go to Stamina, if it's Magicka you kill or heal with, it's Magicka.
If you keep on dying you can try some points on health, but as I mentioned before: base damage derrives from Stamina or Magicka and you want it as high as possible. That also goes for healers, because the amount of your healing also depends on that. There are challenges much, much later in the game where you need a specific amount of health to survive, but since that's for endgame and you also have enchantments and buff food to tinker with attributes, it doesn't matter much in the beginning. For now you may be a glass cannon, but mobs will drop like flies.
Distributing attribute points for Tanks is a little trickier in my experience, because you will use stamina and magicka based skills for support and buffs. Stamina though is also used for blocking, running, breaking free and so on. If you are a stamina based tank divide between stamina and health, though a few more points on stamina won't hurt, especially for single player content where you have to do damage. Should you run out of Magicka to fast, a magicka leech glyph on your weapon might help, or a buff from another source. As I said, it's a bit more tricky. For Magicka based tanks it's the same just swap Stamina and Magicka.
Your first crafted set gear
Once you are familiar with your skills and you made things work for you, you will eventually trip over the crafting system, which I won't explain here. You only need what it produces for you. Only thing that I want to elaborate a bit, is how research and traits work, because those things are closely related to the set crafting stations (don't get me wrong: crafting is awesome and powerful in ESO and you want to be able to do it yourself!).
Crafting stations and traits
Set stations are traitlocked. Means, in order to craft a specific item, you must have a specific number of traits unlocked on it. How many traits you need to be unlocked is defined by the station you want to craft at.
To unlock traits you have to research them, which can be done at crafting stations. You also need an item with that trait, which will be destroyed in the process. Researching has one important catch: it takes a lot of time. The first few traits on an item take a few hours, but the more traits you have unlocked on it, the longer the research times. the ninth trait takes about 2 month or so to research. The timers run while you are offline, so don't worry about that, but you can only research 3 items tops for each craft at the same time, given you maxed out that craft and bought the skill for faster research. It took me almost a year to research all the traits. So you want to begin early.
General gear advice
For tanks you can go for full heavy armour, for all others you should have 5 parts of your main armour type and 1 part each of the others. For a Stamina damage dealer for example it's 5 parts medium armour, 1 part light and 1 part heavy. The reason for that is a passive easily overlooked: "Undaunted mettle" from the Undaunted skill tree. It increases all your attributes by a small amount. It unlocks on rank 7, so in the beginning you won't be able to benefit from it, but well, can't hurt to level up all three armour types from the beginning. The heavy part also provides some additional protection.
Concerning traits I usually go with Infused trait for head, chest and legs because only on those parts an enchantment provides its full bonus, and it can't hurt to furthermore buff it up. For all the other armour parts I go with Divines trait do enhance my Mundus Stone buff. For tanks it's advisable to make one minor part (not chest, head or legs) Sturdy for blocking cost reduction.
For weapons, the Precise trait it very useful. Can't have a high enough crit chance... Also sharpened for softer mobs. Tanks might want to go with Defensive instead and an Infused shield perhaps. Shields aren't defined as weapons, by the way. They share traits and enchantments with armour.
If your character is at the very start of his/her adventure, you might want to use the Training trait for all parts.
Don't underestimate the impact of your gear's quality. It might not make much sense to temper gear in the lower levels, but as soon as you hit 20 or something you should think about that. Green gear that turns more and more blue at lvl 36 or so is a good thing to have.
Quality does not only affect armour rating/damage but also the bonus traits provide.
General "midgame" build advice
The following section is, like everything here, based on my own experience and all the advice I got from ingame friends who know about this stuff. It's, of course, not complete, and I guess people do things differently for different reasons, but it's what I would go with. Never ran a stamina based sorcerer, so you won't find advice for that here. Same goes for *add list of exotic builds here*.
The sets listed here are for "midgame" content, so to say. Some of them also work for some endgame stuff of course, but well, if you advance that far, you will already be more familiar with that topic and start farming fancy sets that only drop in the most brutal veteran dungeons. I still use crafted set gear, except for the jewelry on my tank, and so far that works very well, even for veteran dungeons and things like the veteran Dragonstar Arena and Trials. To be honest, I am also too annoyed by endless farming to really considering superfancy Pro-gamer sets.
Stamina based Tank
I roll very well with:
5 items of Whitestrake's Retribution and 4 parts of Armor Master.The Armor Master setstation is in Imperial City though.
The Whitestrake's set gives you a damage shield that triggers on low health. It saved my ass so many times now, I never would go without it.
Hist Bark can be used as a substitute for Armor Master.
All heavy armour and sword and shield on both bars for most group content. For single player content, and also for some support damage, a secondary weapon is also advisable. For me that is a Greatsword and sometimes a bow for ranged combat, but since you're face to face with bosses anyway most of the time, I'd go for melee first.
Concerning skill choices you should go with skills that buff your resistance traits, regeneration of stamina and health of course. Skills for crowdcontrol in general should always be in your bar. Also take a look at 2 Circle of Protection from the Fighters Guild tree.
Mandatory for a Tank is the second taunting skill. It's 3 Inner Fire from the Undaunted tree. It's a ranged taunt and can be morphed for Stamina use later if you want to try that. To level up the Undaunted tree section you have to do dungeons. So do dungeons until it's unlocked (Delves and Public Group Dungeons work as well). Group content is also the only good way to become familar with tanking.
Mundus Stone is The Serpent for me, for Stamina regeneration.
For more about tanks, magicka and stamina based, you can take a look at Gaius' thread: http://telvanni.guildlaunch.com/forums/viewtopic.php?t=10888506&gid=399833
Stamina based Damage Dealer (especially Nightblades here)
My lovely Killer Bosmer uses:
5 parts of Hunding's Rage and 3/4 parts of Nightmother's Gaze (3 when bow is equipped, 4 when dual wielding)
Instead of Hunding you can also try the Morkuldin set from Wrothgar or Eternal Hunt from Hew's Bane (Poisonous dodgerolling!).
My weapons of choice are two daggers (though I have swords at the moment for some reason... 1 sword, 1 dagger also works well) for dual wielding and a bow. The bow mostly for applying AOE and debuffs, especially on mob groups, Dual Wield for jumping in and slashing until they are all dead. Steel Tornado is the main grinding tool here...
If you are a Nightblade you should slot 1 Assassin's Blade (Assassination) and 2 Veiled Strike (Shadow) early on. Surprise Attack is a main single target damage tool and also reduces its resistance. Also disrupts a target by a stun effect when morphed and you attack from stealth. Veiled strike is your finisher. Do not use it until a mob is on 25% of its health or lower. As soon as it is, spam it, it will also heal you on a kill. There are Morphs for Stamina use for both skills, by the way.
1 Teleport Strike (later Ambush), Assassination tree, is your gap closer and makes you avoid bad stuff and even heavy attacks. It also stuns, and interrupts a target in the process.
4 Mark Target from the Assassination tree is a life saver especially when fighting alone. Just mark one target in a mob group, move in and as soon as it drops, you heal enough to go on killing. Mark another target if there are still too many on their feet.
5 Drain Power (later Power Extraction) from the Siphoning tree is a great AOE damage dispenser, and a real alternative to Steel Tornado. You should also use it at the start of any fight because it gives you a major buff on weapon damage.
Try the following: crouch, mark a target in a mob group, use Teleport Strike (Ambush) and then Assassin's Blade (Surprise Attack) in a quick succession on said target, then use spam Whirlwind (Steel Tornado) or/and Drain Power (Power Extraction). You can sweeten that up with bow AOE before you jump in, but then you don't have that nice execution from stealth I wanted to show you here... Since your group won't find that too amazing, use bow AOE in the field before jumping into groups. ;)
Try around with the rest. Nightblades have many ways to kill people. And they look good while doing so.
Mundus Stone should be The Thief or The Shadow. People say, if your weapon crit is above 50% go for The Shadow for more crit damage, if it's below, go for The Thief for more crit chance.
This is a more advanced guide for a stamina nightblade build which I used: http://tamrielfoundry.com/topic/stamina-nightblade-dps-guide/
Magicka based Damage Dealers
You might want to wear:
5 parts Law of Julianos (setstation is in Wrothgar) and 3 parts of Torug's Pact
If magicka supply is one of your main problems you can try Armor of the Seducer, but you'd miss out on a lot of damage.
Staves should be your weapon of choice. There are people who use other weapons as well without using any of their skills, but well, we keep to staves here since they are the only magicka fueled weapons. Start with a Destruction Staff and go for a Restoration Staff as a secondary weapon. I prefer to have most damaging skills on the Destro bar and buffs, healing and so on on the Resto bar.
So... Fire, Shock or Ice? If you are a Dragon Knight or a Nightblade, preferably also a Dunmer because their racial skills enhance fire damage, it's Fire. For Sorcerers it's Shock, mainly because there is a passive in the Stormcalling tree that grants a chance of disintegrating low health targets by shockdamage. Most advice concerning skills with the Destruction staff are already covered in the "Weapons" section.
Try around with your sorcerer skills and take a look at Crystal shards. These do a lot of damage with the downside of having a long casting time, BUT there is a morph which reduces the casting time dramatically. Anytime you cast a magicka using skill, there is a chance that the shards can be cast instantly. You can see that on your character's hands, which will glow with a Crystal Shard effect thingy for a few seconds. In fights watch your hands and only cast Crystal Shards when you see that glow.
Also: use 1 Mage Light from the Mages Guild tree. Morph it to Inner Light for it's spell crit buffs and keep it on both bars. If you really need a slot in your support bar, kick it, but always keep it in your main bar for damage. It doesn't count as slotted if it's not in the bar you are using.
Magicka fueled Dragon Knights are Fire Mages basically. Most damage they do are based on fire, including many DOTs. Being a Dunmer also helps here because of the racial fire damage buff. Your attack bar is mostly filled with fire. 5 Impulse from the Destruction Staff Tree (morphed to Elemental ring) should be among them. Also keep Inferno (Morphed to Flames of Oblivion) and the Mage Light (morphed to Inner Light) in both bars. For the Flaming whip there is a morph which enhances fire damage even more while slotted, so keep it in the bar.
If you want to know more details or you are looking for a more advanced build, look here:
http://telvanni.guildlaunch.com/forums/viewtopic.php?t=11013424&gid=399833
Thanks to @Calaphot again for providing this build.
Nightblades on magicka should carry a Flame Staff and use a lot of their nasty life drain spells. I didn't play much on a magicka Nightblade to be honest, so I can't give specific advice here. I will edit this section once I know more. Mage Light should be mandatory though (Inner Light morph of course) as well as 5 Impulse (Elemental Ring).
For the Mundus Stone you can go with The Thief or The Shadow, or the Mage for more max Magicka.
Healer
So far I only experienced Magicka fueled healers. Try using:
5 parts of Law of Julianos (setstation is in Wrothgar) and 3 parts of Torug's Pact
Templar is the most natural class for healers, because they have a class skill tree dedicated to it. I didn't try anything else so far, but somebody told me, that also Nightblade can be good healers due to their life stealing and siphoning abilities. Well, can't provide any specific advice on that though.
What all healers have in common is a Restoration Staff. I would also recommend a Destruction Staff for "self defense" and damage support when needed. I already described the most useful skills in the "Weapons" section of this guide, so you can look it up there.
For my Templar healer I love 1 Rushed Ceremony (Breath of Life morph) from the Restoring Light tree. It's an instant heal for 2 people.. The Ultimate of that tree is also very useful if you run out of magicka or you need a quick overheal. Try around with the rest and be sure to morph 3 Restoring Aura into Repentance. Your tank and stamina DDs will love you for that. Stamina siphoned from the dead. Who isn't into things like that?
Also for delivering more Stamina to your group you should regularly throw Spear Shards, morphed to Luminous Shards. The Synergy allows others to restore Stamina.
For a Mundus Stone you should try The Mage, for more Magicka or The Ritual for more healing (especially if you are low on Champion points since you won't be able to increas your healing by those).
Disclaimer:
This is based on my experience and knowledge of game mechanics. I do not claim this to be the only way things can be done. It reflects what I tell people if I am asked ingame. If you are looking for more advanced information, builds for endgame content and things like that, this guide will not suffice.
Also: You may of course post any further advice on my guide itself as long as it's fitting in, and I am also glad for corrections in case I screwed something up.
Please do NOT post any advanced builds, lists of farm locations for endgame sets or stuff like that. Your knowledge would be pretty much wasted in this section. I hereby declare you responsible for sharing your knowledge in another thread or be silent. The "Research and Debate" section of the Forum is made for things like that. Thank you.