Make sure that your cat has multiple escape routes from the box, and that it is difficult for another pet or person to sneak up on her while she's in the box. (cat-lovers-only.com)
The area should be quiet, away from the food and water bowls, and preferably should allow for multiple escape routes. (cat-lovers-only.com)
These locations should also have multiple escape routes so that your cat can quickly leave her litter box if she suddenly feels anxious. (aspca.org)