To easily level up you skills for blade, blunt, destruction, restoration, mysticism, marksman, hand to hand and conjuration head to the Arena and get to the point of being a champion where all you have left to do is fight the grand champion. Do not fight him yet though!

When you talk to him decline challenging him and talk to him about himself and you will be given the Grey Prince quest, after you finish the Grey Prince quest fight the grand champion.

Since doing this quest the grand champion will come out of the gate, take one swing and then tell you to kill him. Now press start go to options and turn the difficulty all the way up and the Grand champion will have tons of health and not attack you no matter what you do to him, keep a heal on target or touch spell on hand so you can keep casting spells on him and whatnot,

When doing marksman try sneaking until he cant see you and your marksman, as far as I know it will go up a lot - same thing with blade and blunt, just make sure to not kill him early.