First, you will need to ensure that the location of the litter tray meets all of the criteria to make it an appealing spot, being careful not to hide it.
In a nook of a utility room or garage is ideal, somewhere near the cat flap might be good too. It doesn’t matter if the tray is in an area with less heating than the main parts of the house. The cat will not spend much time there and they are perfectly prepared to go outside, so the shelter of a garage is almost considered a luxury.
The corner of a bedroom is not a bad place to start with a litter tray, but the associated smells can sometimes be unpleasant, so you might not want it in the bedroom for longer than necessary.
Wherever you put it, make sure you put some newspaper down underneath it – even the most well-trained cats can sometimes have ‘boundary issues’!