for when ppl come over, make it convenient to get rid of things...ie. put waste baskets 1/room and more in the living room [by the sofa, or chairs, i have no clue what your interior looks like but put it where you know ppl gather the most], if you have a coffee table, regular table, leave nothing on it so there's more room for dishes on the tables rather than the floor, making clean up easier.
with your roomies, make a deal that the two of you who are clean, clean. The other two can pay for groceries more or something else equally helpful. People rarely change their habits and stick to it, if they can't...find a way to make it more fair and square by other means.
Finally for the carpet, if you guys have money, invest in a very fancy carpet cleaner or vacuum [is it stains typically?], like those dirt devils or one of those industrial grade type things. Or else line the carpet with newspaper before ppl come
jk...god i hate vacuuming, the best thing is to get hardwood/linoleum floors.
*/ martha stewartness*