I will mainly be talking about mages... considering they are the most complex but i will add the fighters, theives, and assassins later.

MAGES:
Items: I ALWAYS ALWAYS rush to get Morokei... a dragon priest mask and Archmages robes, both found while doing the Mages College quests. Archmages robes adds an awesome 15% reduction to all costs, gives you 50 more magicka, and 100% magicka regen... which is SO VERY USEFULL FOR A MAGE. Morokei is mainly for a little armor and it's 100% magicka regen.

Races: Altmer. they are so overpowered mages they have a crowd control spell: Fury from level 1... Dunmer: alright... could use some work but they have fire resistance which is nice they have Sparks off the rip... Breton: great mages... they have MR (magic resist) from their Dragonskin power and they have a Familiar spell right off the rip from level 1... so just send the pet off at whatever and pick the enemies off from a safe distance.
(****ALL THE OTHER RACES ARE GARBAGE MAGES****)

Perks: first, i try my best to just rush to get the master perk of the school. if you are good, you can summon a Dremora Lord and train your skills on it. (HINT: kill a goat, then cast soul trap on it until you get 100 in your Conjuration... found this little cheat while derping around) get the silent spellcasting perk from the Illusion school so you can sneak attack things and get Destruction... as its a mages only way to kill. Just max out all the perks for the schools of magic.

Strategies: Mages need magicka. Get at least 500 base magicka (without item effects) to even consider yourself to be a mage. Since mages are going to be weaker... get good at mage armor: Oakflesh, Stoneflesh, Ironflesh, Ebonyflesh, Dragonhide. To initiate cast one of those. Then i get a daedra of a sort, usually a dremora lord or sometimes a frost atronach. Then use destruction spells according to the enemies class: Mages: Shock, Fighters: Frost, Theives: Fire. If wanted i put a wall of flames around my mage and if anything comes too close, i cast Paralyze on them so they are stuck on the wall taking heat and i gun them down while they are dieing on the wall.

Stones: I generally get the Atronach stone for more magicka and magick absorbing. Morokei and Archmages robes makes up for the stunted magicka it gives you. At first, i would get the Mage stone at the early game and get good at my spells (like 50 in all the schools or more) and then transition to The Atronach stone for the large pool of magicka it gives you.

**** Important things to remember**** A mage is weak. dont fight them by yourself, summon some monster to take the damage, if not possible, use the shout: Whirlwind Sprint and get out of there. A mage is only as good as his/her spells. Let's face it, you need to upgrade illusion whenever possible and take advantage of the crowd control. i generally dont fear because it leaves you having to chase them down. Also get the perk Master of the Mind in Illusion so you can cast Courage or Rally on your Daedra or Undead. Also get the augmented shock, frost, and fire perks to upgrade your damage on the spells.

Or 100% cost reduction. Investing in magicka is a waste with that. Unless they changed it with a patch recently.

Important things to remember: This is a single player game and if you're focusing on min/maxing, you need to give some thought to whether or not you're having fun. Some people have fun like that. I prefer roleplaying. You're only competing with yourself.

Another thing to consider is that for those not looking to roleplay but simply get as powerful as possible even if it means cheating. For anyone playing on the PC it's easy enough just to give yourself godlike powers with the console. Fair enough for those playing on consoles I guess.