There a few tricks to setting up a kitty litter routine.
For cats, as well as people, the toilet is a very personal place. Just as we don't want an audience on the loo, your cats need privacy too. When picking the perfect place for a cat to pee, find somewhere that's quiet and doesn't get a lot of traffic.
The tray needs to be big enough for your cat to be able to squat and dig comfortably.
Cats are creatures of habit, so stick to the same location and kitty litter that they're accustomed to, or your kitty will start searching for their own toilet spot.
One of the biggest mistakes that people make is not having enough in the tray. You see in a multiple cat household, you need multiple trays, one per cat plus a spare, that way they're never caught short.