#1: Do not fall to the pitfall of choosing a class purely based on the role you play. Ex. A tank like character would be Dragonknight, healer a templar, mage a sorcerer and a bow character Nightblade. Currently out of the skills we know so far, none of the classes has designated skill trees. As such every class has a broad range of abilities. Don't suffocate your imagination based on other peoples hypothesis of trinities, they won't exist here by standard.

#2: If you plan to lean heavily on something, example: stuns, you absolutely do not require 3 stun abilities. Remember that we have zero cool downs, so you do not need to rotate 3 stuns on your enemy.

#3: Every class will be as efficient with every weapon and armor class, the passives will remain the same. You absolutely are not required to pick a Dragonknight or Templar if you want to use heavy armors. Naturally some classes have abilities that synergize better with certain weapon or armor class, but out of the broad range of skills we have, it is more than likely everyone will have good stuff regarding others.

#4: The common misconception of Nightblades. Currently it has been stated stealth tree is tied to medium armor. And it would be against the Zenimax's vision to restrict stealth as specialization to one class (in this case; Nightblade). Hold your breath, we'll know more details sooner or later. Just don't blindly fall to the trap that a stealth character HAS to be an nightblade. It is more than likely that nightblade won't have a designated skill tree line (why would it? Because of the name-sake? Sorcerer is known to possess destruction, well ta-da that is tied to a weapon skill)

#5: Min-maxing will be impossible. Stop thinking if you roll a DK you will have the min-maxed character regarding survivability. Because of large amounts of skill choices, each build will have their strengths and weaknesses, and none will be the absolute cookie-cutter. Imagine Rock, paper & scissors. Except that with dozens of rock varities, dozens of different paper types and dozens of different brands of scissors. We are incapable of getting every single passive and ability. Or well, we are; Its that we cannot use all of them at one time.

#6: The pitfall of race selection; We have absolutely no darn idea of the racial skill lines, it is not exactly sure if they will even exist at this point, all talk has been speculative. Your Khajiit won't by standard be a better choice for a sneaky character than Altmer.

#7: Narrow-minded thinking. Survivability does not equal stacking health. Nuker role does not equal maximizing your damage output. Healer / support role does not equal maximized healing output. The game is in a role where a viable character will possess control abilities, counters to said control abilities and few other utility skills. Everyone can pick one or two standard nukes and be capable of dealing damage. A character that deals a bit less damage but has tons of more utility will always be a more viable choice over a character that deals higher amount of damage but has absolutely no utility.

#8: Blindly listening to others. Someone claims they have found the best build ever? Use your head, if they had indeed found such build, would they share it voluntarily? No, they would not. Out of MMORPG class build guides, 99.99% are of average or below average level. MMORPG gamers unfortunately can be categorized in a way that more than three out of four have extremely biased views that are full of misconceptions, ill information and lack of out of box thinking or that of common sense. Try the builds yourself, see what suits your playstyle. Don't find the first guide thats labeled "Best Templar healer build of all time" and go for that, as it is more than likely that the build shines as mediocre at best.

Sources; Official information, leaked content, MMORPG experience and common sense.