Select an appropriate style box and substrate. Boxes should be large enough for your cat to stretch out full length and still be confined within the box.
Adhere to a strict cleaning schedule:
Scoop all boxes twice daily.
Dump out litter, clean the box with mild soap and water, and refill with fresh litter every 1 - 2 weeks.
Completely replace boxes every year.
Provide at least 1 litter box at all core locations: resting areas, feeding areas, etc.
Place litter boxes in a location that has multiple entrances and exits (ie- not in a small bathroom corner).
Provide a box in any areas where your cat is currently eliminating undesirably.
Should your cat eliminate outside the box, use an appropriate enzymatic cleaner.