(buy this at Home Depot or any home improvement store for around $10)
Brush with a Handle or Sponge Mop
Carpet Cleaning Foam
(Bissell is 1/2 the price of Resolve where I live but you can use any brand)
If you have pet stains you'll also need this:
If you have pet stains, spray the pet stain remover on them heavily enough to saturate, blot, and brush in.
in this one, but you can still see the difference)
(click to enlarge)
once every three months and I would still recommend having carpets cleaned professionally about once every 1-2 years.