Acclimate them to being handled. Conditioning your cat to having their paws touched is essential before you attempt to cut their claws, and this takes time. Focus on a single paw, or even just a single or double toe, at a time.
To make things easier, have another responsible adult hold the cat. You can next devote your full attention to clipping the claws.
To keep your cat still while you clip its nails, gently wrap its body in a towel. Simply extend one foot at a time from the towel's confines.
Plan on trimming when your cat is relaxed and sleepy, like just after dinner, since this will make the process go more smoothly. That ought to render them more manageable.
No matter the type, your trimmers should always be sharp. Trimmers with a dull blade will only create a partial or ragged incision, whereas a sharp one will make a clean one.
While you're grooming your cat's fur, reward it often. They can be bribed into cooperation with a lick of tuna or another tasty treat.