Trim a little at a time, avoid the quick, and pair each paw with treats.

Use pet nail clippers or a grinder. In light nails, avoid the pink quick; in dark nails, trim tiny amounts and look for a pale oval center.
Handle paws daily before cutting so touch feels normal. Clip one or two nails per session if your pet is nervous.
Keep styptic powder nearby in case you nick the quick. If nails are very overgrown, ask a groomer or vet for help.