You should have one more litter box than the number of cats you have (ex. 2 cats = 3 litter boxes).
The boxes should not all be in one place (if you have stairs, at least one on each level) and need to be in a private, quiet area.
Make sure your litter boxes are large.
Most cats prefer boxes that are NOT hooded.
Make sure the litter is at least 3-4 inches deep at all times.
Most cats prefer unscented, perfume-free,clumpable litter (Dr. Elsey’s Precious Cat Litter is excellent).
Completely dump out and wash the litter boxes with a mild soap (not bleach or ammonia) every 2-4 weeks.