Brush your cat. Do not skip this step. Brushing the cat will help remove any knots and tangles in the fur, which will be much more difficult and painful to remove once your cat is wet. If your kitty likes getting brushed, then you can use the brush to make the kitty feel more at home in the tub.[2]
Sometimes you can even brush your cat as a way to distract her enough to allow her nails to be trimmed. This is a great way of killing two birds with one stone, but you'll need another person to help you.
Get the right cat shampoo. You can get kitty shampoo from your vet or local pet store. Check the instructions to see if it's right for your cat, and dilute it with water if necessary. Using regular human shampoo can not only dry out your cat's skin but can be toxic for your cat. Don't use dog shampoo in a pinch, either. You're better off using water rather than a product that can harm your cat.[3]
You may want a washcloth for massaging the shampoo onto your cat's body, but your hands may actually be better for this.