Whenever you need to make corrections on your dog’s actions, you should make it as clear as possible. Aside from that, it should also be short and well defined.
By doing it this way, you would be preventing your dog from getting confused. Aside from that, it would also make him remember the corrections better.
Use one syllable word commands at the beginning.
If you have just started training your dog, you should see to it that you are giving commands that have one syllable only.
For example, instead of using sit down, you should use sit, so that it would be easier to understand and remember for him. Do it this way, so that your dog won’t have difficulties in following what you want.