Lower the difficulty down to zero. Put on 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, you can try letting 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 joining the Blades as part of the main quest, attack one of the other Blades so that they will attack you. Do not kill 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 afterwards.