I can't tell you how many times I've seen someone trying to teach a puppy to sit, only to totally confuse the puppy. It's like this : "Sit", "NO", "Sit"," Sit Down", NO!," Sit", "Sit Down Bowser" "Come on, SIT". And they wonder WHY the dog doesn't understand the command. Be precise and clear about what you want your bird dog to do. Use one word commands, and simply repeat the word, instead of also telling him NO! when he doesn't sit. At first, you can push his rear end down, saying the word "sit" at the same time. This shows him what you want him to do. As soon as he sits, immediately reward him.