First be sure to trim down all the hair between the toes, as these can mat easily and possibly cause pain.
Then trim the nails.
Dog's nails can be self-trimming to different degrees depending on the type of surface they walk on and how rigorously they do so.
If they spend much time on rough concrete, such as taking frequent brisk walks around the block, then the need to trim the nails will be minimal, as the ground will wear the nails down.
If they hardly get to walk on a rough surface, and spend all their time on carpet or wood, then nail trimming will certainly need to be more frequent.
Ideally, nails should be trimmed as far back as possible because short nails are the most comfortable for your Peke to walk on.
Understandably, however, many owners will be afraid to cut into the "quick," which is the vein that runs through each nail;
cutting into this can be quite painful to the dog.
When in doubt, trim a little at a time.
If you feel the veins in your dog's nails extend too closely to the tips, trimming in small amounts will encourage them to retreat and gradually become shorter.