How should my roommates and I go about chores?

okay, i'm getting ready to move into an apartment in about a month with 2 of my really good friends. but i don't know how to go about chores and things. obviously dishes can be done as used. and most things are clean up after yourselves. but what about sweeping, mopping, and vacuuming and stuff. how should we divide that up? also, how should we do groceries? should we all buy separate? or go in together for everything? help is appreciated!