Cavalier King Charles Spaniels are a “Double Coated” Breed:
Double-coated Cavalier King Charles Spaniels have both a topcoat of longer guard hairs and a soft, thicker undercoat.
As the weather turns warmer, rake your Cavalier’s undercoat with a deshedding tool to clear out the thickness of your dog’s undercoat. When the undercoat is thinned out, air circulates more freely between the hairs of the top coat and keeps your Cavalier cooler. Weekly brushing and avoid shaving will cause the coat to thicken, curl and makes it dull, so I don't recommend this.
Brushing around ears daily to weekly to prevent the common matted areas
Trimming the fur underneath the paw to prevent slipping and improve better grip
Grooming professionally spring and fall to help during the natural seasonal occurance of "blowing their coat".
Wiping in corners of their eyes daily will help keep them clean.