If your dog is emitting sit on the first approximation (first time) you ask for it, move on to the next behavior. Down can be difficult for some dogs so work slowly. First ask your dog to sit say good (or any positive word) then reinforce that. With your dog still sitting get another treat say the word down and move your treat down to floor. if your dog moves his head downward take that, say good and reinforce. Now do it again but move your hand further down if your dog leans down further reinforce that. Now the next time when you start bringing your hand down to floor, say down and move your hand away from the dog on the floor. If he starts crawling down to get the treat, say good and reinforce that. This is called using small approximations or steps to get desired results. Dont expect your dog to just lay down. lean him down through positive reinforcement. I know some dogs just seem to get “down” but this method is great for dogs who just need more guidance. Remember also to always end on a positive. If your dog has improved at all after a few sessions stop and give them a play. Then after some time start again. Your dog will learn down in a day if you work on it in small positive steps. Anytime you dog doesn’t do what you want, ignore the behavior and ask again. Reinforce only improvements!!