First, what is your marker? A marker is the indicator that your dog has accomplished the task you have ordered. It can be yes (my marker), or a clicker, and I'm sure there are others. It is given immediately when the motion is complete.
Second, what is the reward? Food is a powerful motivator. Try putting food in your hand while sitting and lead the nose down while giving the down command, mark it, and give the reward. Next, lead the nose up while giving the sit command, mark it, and give the reward.
Markers are important. They make it clear the dog has completed the motion, and the reward helps with the motivation.