One great site for this, IMO, is
www.flylady.net
It gives you clear routines and advice on how to start, and has really helped a lot of people!
For me, the biggest thing is not letting my house ever get to a point where I would be uncomfortable having anyone over to spend the night without more than 1 hour worth of cleaning time. That's my particular guideline - if it would take me more than an hour to get company-ready, the house needs to be cleaned ASAP. It's a good limit for me...gives me the flexibility during a busy week to let things get a bit messy, but prevents me from getting out of hand.