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, have at least one litter box on each level of the home) 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 os at least 3-4 inches deep at all times.
Most cats prefer unscented, perfume-free, clumpable litter (Dr. Elsey’s Precious Cat Cat Litter is excellent).
Completely dump out and wash the litter boxes with mild soap (not bleach or ammonia) every 2-4 weeks.