Depends on what breed you have. If you have already had it groomed at least you will know what it should look like. I bought clippers several years ago and they had a video and booklet desribing how to groom/clip a poodle, thingyer spaniel and snauzer (not sure about that spelling). I think the clippers were Oster but am not sure. Usually a pet store will have small booklets on each bread, Mongrels I guess you would either mimmick the predominent breed or just wing it until you had a dog you could live with!