I clip my cats' claws when they need it, the vet showed me how to do it. Mine scratch trees and fences and spend a lot of time outside, but still have strong sharp claws and are - like Lizzie - big strapping cats, so sometimes don't know their own strength - and catch in carpets, my clothes, furniture - etc. No 1Son has particularly sharp pointy claws so I have to attend to his regularly. You need a strong pair of toenail clippers, and to hold the cat very firmly with his toes splayed, it can be a 2-person job, or to be done in several stages! A cat's claw has the quick quite near to the end and you must not cut into that, you really do have to take care as damaging the nail is serious - so I usually clip the end off only, no more than the really sharp end 2 mm. if your cat is smaller, then probably a millimetre will do - it really is just to take off the sharp pointy bit. Don't forget the dew claw too, but be equally careful with that. Back claws don't need attention - only the front paws.
I know others will feel differently about this but having had instruction - and the three cats needing a manicure - once the vet showed me how to do it, I've done it for years, about twice a year. If you are not happy or not confident, please do seek vet advice.