Once a week for shorthaired cats should be sufficient, whereas longhairs ideally need daily attention. The more often you do it, the easier and quicker it is to keep the coat tangle-free, glossy and looking good. You need to pick your moment when to groom – waking the cat up to do it is not a good idea, and neither is grooming when he is fractious or unsettled for some reason. If your cat becomes fidgety and stressed by grooming because he was not accustomed to it from an early age, then do it little and often to gradually get him used to the procedure.
Never force the cat to be groomed; wait until he is in an amenable mood before trying again. Offering tiny morsels of his favourite food can help settle him and take his mind off what you are doing, as well as help him to associate grooming with something rewarding and pleasurable.
Having someone help by holding the cat can sometimes prove useful – they can talk to him and offer treats to distract him while you concentrate on the grooming.