Contrary to what you might think when seeing the silky, way coat there are not many Cavalier King Charles Spaniel grooming styles. Most owners, especially if the dog is being shown, do not touch the coat. With regular brushing it stays in great shape so Cavs do not need haircuts or clipping.
Sometimes trimming is necessary. For those wondering how to trim a Cavalier King Charles there is an important fact to note. Show dogs aren't allowed any trimming other than the feet. Using a pair or canine scissors to cut the hair between the toes is usually allowed. Non show dogs also often have the feathering on their ears and legs scissored. There is no specified length on this.
Some owner want their Cavalier King Charles Spaniel hair cut short, especially in the summer. Puppy cuts are popular for many breeds and offer a less attractive (but lower maintenance) style for the coat. This involves using a pair of clippers to cut the coat down to one uniform length. Be warned, a shaved Cavalier King Charles Spaniel will not have the same regal look and vibrant coat color as one whose coat is left natural. The grooming styles pictures on this page should give you a good idea of the difference between a puppy cut and non shaved Cavalier.