My cocker spaniel is deaf. She is 13 years old though and just recently went deaf. I was in obedience with her though in her younger years and taught her hand signals and had to do trial work with no verbal commands at all.
I'm so glad I did it because it makes it so much easier. I'm going to start teaching all mine hand signals. A couple of them know them already by just watching the others, it really is amazing how smart dogs are and how they can pick up on things.
Usually I just tap her or walk in front of her to get her attention so she can see what I want.
I don't know what I will do if she goes blind. Hopefully it won't come to that for a long time.
For one that is deaf to begin with prior to learning hand signals you would have to show them what you want. For example give the hand signal for sit first and then make the dog sit and then give them a treat. They will pick up what the hand signal means in no time.
Here is a video that shows you some hand signals. My hand signal for sit is a little different than theirs but the others are the same. You can use any signal you want you just have to be consistent but I thought this would give you an idea. I also have a hand signal for stand, fetch, left, right, shake, roll over and take a bow.