A well-conditioned coat is a combination of two things: genetics and diet.
Rabbits purchased from reputable show breeders will have thick, luscious coats that feel especially smooth because of the breeder's efforts to select for a balanced, well-fleshed animal. You wouldn't think genetics could play such a large role, but show rabbits feel drastically different than rabbits bred for pets or "oops" litters and the like.
Diet is really important too. Some people push low protein diets which are not necessarily best for the domesticated rabbits of today. I feed the same amount protein (16-18%) to all my rabbits - show/breeding and pets. Their pellets are the main source of that, and pellets are supplemented by mixed grass hay for fiber intake. I don't add anything else to my feed. However, some breeders will up protein a bit more before a show with oats, BOSS, oils, etc.
The combination of these things is what has to come together for the best body and coat condition. A well-bred rabbit on a poor diet will rapidly lose condition, just as a good diet can improve the condition of a poorly-bred rabbit. The balance is what you have to find, and a lot of that is trial and error - what works best for your bunnies.