How can you encourage others in your household to also clean up after themselves?

Give them compliments for being so good at tidying after them selves. I know from my psychology books, that if I'm consistent in giving compliments, they will actually do more of the good stuff.

I could show them what I do, in order to be a good example for them. Also, I may help them , so they will be inspired to do so. And show how comfortable is to live in clean environment.