Special nail clippers designed to be used with only one hand are available. Also, depending on the strength in your affected hand, you might want to try foot-operated clippers.
To file fingernails, tape a nail file to a table and run your fingers over it.
Cut and file toenails after soaking them in warm water. The water helps soften the nail. If you have a reclining chair, put your feet up on the extension when you clip your toenails.