Do Collies smell? While not especially known for their "doggy odor," these dogs can get funky without consistent bathing, especially if they spend a lot of time outdoors. Overall, though, baths are only necessary every 2-3 months, unless your Collie is particularly grimy.
It's important to use canine shampoo (and for Rough coats, conditioner too) with your Collie bath, as the kind made for humans has a different pH and will irritate a dog's skin. Some owners like to use a 2-in-1 shampoo and conditioner combo. The best shampoo for Collies includes brands like Buddy Wash, Earthbath, and 4-Legger, most of which have 2-in-1 combo products.
How to bathe a Collie: first give the coat a good brushing. You can bathe your Collie either in a bathtub (hopefully with a spray nozzle attachment), or in an outdoor plastic pool using a garden hose. Wet the coat thoroughly, then apply some Collie shampoo to the dog's back. Lather well, working downward and outward as you go. (And don't forget the legs, underbelly, and tail!) Clean the face, head, and ears with a washcloth, then rinse the coat completely. (Then, for Rough Collies, you can repeat the entire process with conditioner.)
Towel-dry the coat next. With Rough coats, you can then use a hair dryer on its lowest setting to continue drying, brushing the long hair out with the pin brush as you dry; Smooths will be fine air-drying. Finish with another quick brush-through to make the coat look clean and neat.