Dogs can be such a special part of any family. Many people consider them like four legged children, and just like children they require assistance grooming themselves. Toenail trimming is vitally important to maintaining a dog's health and comfort, but quite often overlooked until they start causing the dog issues.
When a dogs nails get too long they can get caught on things and can be ripped out or broken into the quick, both of which are very painful. Also if a dogs nails are left overgrown for too long it can start to change the bone structure of the dogs feet, flattening them out and/or even twisting the toes.
How often a dogs nails need to be clipped depends on how quick the digs nails grow, how active the dog is and what kind of surfaces the dog walks and runs on. Rough surfaces like cement keep a dogs nails filed down so they need clipping less often. Smooth surfaces like tile are not going to have any kind of filing effects so the nails will likely need clipped once every month or two.
When it comes to actually clipping the nails the most important thing is to avoid clipping into the quick, or sensitive blood vessel at the base of each nail. White nails are much easier because the pink is generally quite visible so you just clip a little before the pink area. Black nails are more difficult because more often than not you have to try to pinpoint the quick based on where the nail begins to look hollow. For most people this is a job best left to the professionals like veterinarians and groomers.