If as you get on the horse is resisting by backing up,then practice backing up!
Soon the horse will tire of backing up and look for another way to avoid the task at hand.
Sorry,but this is what training is all about sometimes.
Circles also help in some cases.
Locking on to other horses can get the horse moving and help them get the idea to move out in the beginning and it is important to keep the feet moving.
I usually slap my leg or wiggle the split reins toward their rear end a bit to get some forward movement,but if that is not enough,then you might consider what others have suggested and stay a little closer to home until you have some of the basics worked out.
"The greatest strength is gentleness."
- Iroquois Proverb