Assuming you have the latest patch, removing the Ogmah Infinitum glitch and the Persuasion loop with the guy in Riften, the fastest way to do this is with Alteration.
The first this you need to do is obtain the Detect Life spell. This is easily done by going to Treva's Watch and completing the quest there. Then go to Riften and channel the spell with both hands while there's a crowd at the center of town, mainly midday. This should increase your Alteration very quickly.
There are also a few other ways that are easier, but more time consuming:
Level Sneak by sneaking into a corner without being detected. You'll have to put the controller on something to keep your character moving, and it'll take a long time, but it should work.
Level Conjuration by casting Soul Trap on a dead body.
Level Alchemy by making potions with very high Fortify Restoration enchantments. Note that getting enchantments high enough could take until you get your Enchantment stat up rather high.