Take pictures when you're done. If you have a bulletin board, print them and put them up there to visually remind yourself of what the clean house looks like. If not, you can print a couple and put them on the inside of the kitchen cabinet doors. Seeing the fruits of your labors is very motivating to not let it get recluttered. And when life brings more clutter your way, the pictures remind you that you can do it, and it's not an impossible task.