Just find your level and choose the right Episode that would give you the highest % of EXP pts (within your ability to complete the episode, of course). Obviously, you would prefer to do the episodes in red because they give you 9-14%, but because of their high difficulty, you will have to join another group or ask a higher level buddy to complete the episode with you, cuz you WILL die many times (Make SURE to respawn/continue immediately, by clicking the middle tab on the "CONTINUE?" countdown screen). Of course, the best way to LU is to join your higher level buddies in those really difficult eps, but if you're alone online, then use this chart so you can increase your Power in little time as possible.
Ummm, yeah... I made this table for the current Grade/Year that I am in (Year 2) for those at Power Levels 18 to 46 (I'm lvl 22). However, I will be making the other ones soon. Sorry if the pics are too high in resolution... Let me know if I should change anything.

This one is to assist in finding the Episodes more easily. It cross-references the Eps # to the pictures of the actual Eps in the YG Eps Lobby. Use amfest's handy "Episode Year List for printout"

Note: ALL the above info in the 2 pics has been taken directly from the website: http://yogurting.s140.org
Great job guys!
And a big thanks to Pounce and Smithy for all their in-game tips and advice for dumb@sses like me to have more fun in this addictive game.