Are you that lazy like I am? Awesome, because I need more friends. Just kidding.
ANYWAYS: Down to the tutorial.
REQUIRE
Mod: TooManyItems
Decent Reaction Time
HOW TO LEVEL UP QUICKLY:
1: Go into Minecraft and make a little pit that is surrounded on all 4 sides.
-- Make it so that the pit is surrounded by 10 block (height) walls.
2: Go into Creative Mode (if you aren't already) and fly into the pit, but DO NOT land at the bottom.
3: Put 4 - 6 batches of 64 Pig Zombie spawn eggs.
4: Depending on how bad your computer is, try to aim for spawning 2 - 3 batches at a time.
5: Once you are finished spawning, exit creative mode and get 2 - 3 batches of potions.
-- I prefer using the best Instant Health potions.
6: Fly up JUST high enough that the Pig Zombies can't touch you.
7: Aim down with the potions and hold right click until they're all dead.
8: Flip back into creative mode and fly to the bottom of the pit and receive a ton of experience! And all the drops that no one really needs.
VOILA!
If completed correctly, you will get a load of experience. From my personal experience with this method, I was level 21, did 2 batches of those eggs, killed them all by potions, and was levelled to level 27.
Images and possibly tutorial video will be posted later.