It might be said that the litter box is the most important item, to both the cat and her owner. The last thing that any cat owner wants is for the cat to decide, for whatever reason, to not use the litter box. It’s not like the cat can magically stop peeing and pooping, so if she’s not using the box she’ll be peeing and pooping somewhere else, somewhere that her owner definitely does not want to find pee or poop.
So your number one rule should be to make the litter box as easy and inviting to use as possible, and to give your cat as few reasons to avoid the box as possible.
Pretty much any cat or kitten that you get from a breeder or shelter will already by litter box “trained”. It really doesn’t take any training for a cat to want to use the box; it’s instinctive for them to want to be able to bury their waste, so they naturally favor the box and litter over a hard floor or carpet. Any teaching that is needed is usually done by their mommy cat.
Get a large litter box
Don’t try to economize, on either money or space, by getting a small box. The average cat is around 18 inches (46 cm) long, the box should be at least several inches longer, at least 22 inches (56 cm) minimum, but larger is even better. Cats need to be able to scratch around in their littler, most like to dig a hole before doing their business and want to do some burying afterwards. So give her lots of room in which to do that.
Type of box
At least to start with, just get a big, plain, simple box. Don’t get a covered box. Cats are a prey species, they have instincts about protecting themselves from being attacked. The act of peeing and pooping inherently makes them vulnerable, so cats often feel like they need to have an escape route; a covered box takes that away. Also, some cats like to use the very corners of the box; a cover makes that difficult.
After a few weeks of your cat faithfully using the box, you can try putting a cover on it if you must. But be on the lookout for “accidents”. If the cat pees or poops outside the box, anywhere, she is telling you that she doesn’t like the cover. Take it off immediately!
For the same reason, don’t start right out with any of the fancy self-cleaning litter boxes. Many of them are covered, or make it more difficult for the cat to get into and out of. And the self-cleaning mechanism can scare the cat, even if she’s not in the box at the time. Being nearby when the mechanism starts up, seeing her box move, or hearing her box make loud, strange, scary noises can all give your cat a reason to avoid it. So again, start simple, wait a few weeks to make sure your cat is comfortable with using the box, then you try a different box. Be sure to watch carefully to see how your cat reacts to it.
Placement
Put the box somewhere that your cat can easily get to it. I know no one likes to look at a litter box, but don’t hide it so well that your cat won’t want to use it. For the same reason that you shouldn’t start out with a covered box, don’t start out by putting the box in a cupboard or some other isolated place with no escape routes.
After a few weeks, when your new cat is settled in and has been using the box regularly, then (if you must) you can try a covered box or try moving the box into a cupboard, or whatever other changes you want.
But be watchful for the first few days after any change. If your cat stops using the box, she is telling you that she doesn’t like the change, so put it back the way it was!
First thing with a new cat
After you get the litter box set up, filled with litter, and put in the place where you are going to keep it, take your new cat and gently set her into the box. Most likely she will just jump right out because she doesn’t need to use the box right then. But what you’re doing is showing her where the box is and what it’s filled with. It may not look like she paid it any attention, but now she knows it’s there and most likely will go to it when she needs to go.
Cleaning the box
Scoop the waste out of the box at least once every day or two, more often if you have more than one cat. It is not necessary to empty the box or wash it or disinfect it. Indeed, doing a thorough cleaning of the box might be counter-productive. If you just scoop out the waste, the litter will retain some of the cat’s scent. This will tell the cat, “Yeah, this is my box, I can use it.” On the other hand, a totally disinfected box with brand new litter might be off-putting and cause her to look for somewhere else to go.
Type of litter
I won’t recommend any brand or type of litter. There are too many choices; clay, walnut, pine, newspaper, silica, clumping, not clumping, etc. Nothing I could say will be right for every owner and every cat. The single most important thing, just to repeat myself, is that your cat wants to use the box. So find a litter that your cat likes.
If accidents happen
If, heaven forbid, your new cat doesn’t use the box, don’t just give up, you need to find out why. Try a bigger box. Try changing the type of litter. Try moving it. Put the box in the place that the cat has decided to go.
There are lots and lots of reasons why a cat will avoid the litter box, or will stop using a box that she has previously used. It is far too complex a topic for me to cover here. Do some searching on the web and you will find no shortage of help and suggestions.