Collies have either rough or smooth coats, but the under coat is always soft, dense and abundant. The outer coat on smooth Collies is hard, short and of course, smooth to the touch. The coat is thick, but it lies flat against the body. Rough-coated Collies have an abundant long coat that is harsh and full, especially around the mane and ruff. It can be wavy or straight, but it should not be curly. The hair around the face, muzzle and lower legs is always short, smooth and soft. Collies have long tails that are covered profusely in hair on rough-coated varieties. Most people picture sable Collies like Lassie, but they also come in tricolour ( black, tan & white), & blue merle patterns. Still, the black, white and tan variations are very popular, and all Collies have traces of these colors in their coats. Collies also need to be bathed, because those beautiful coats can collect debris. Use a conditioning or detangling dog shampoo about once every six weeks. 

Further information including a step by step pictorial guide can be found at

http://eagermind.wordpress.com/grooming/grooming/