-After lowering the difficulty down to zero, equip your heavy armor and let a weak monster (such as a rat) pummel you. When your health gets low, heal yourself (this also helps with Restoration). When you get strong enough, let a human hit you. You will level up about every ten to fifty seconds, depending on how many monsters or people are hitting you.
-After you join the Blades as part of the main quest, attack one of the other Blades so that they will attack you. Instead of killing them, let them attack you without blocking and your armor level will skyrocket as compared to normal combat. If you can, restore your health with magic or food. When ready to stop, yield and they will stop attacking. Go into the west wing and sleep to heal and level. Note: There is a hefty fine afterward.