There's no shortage of drills, exercises, and tests you can perform to both gauge your balance and improve it. Dr. Toole has this advice:
When you come to a potential balance-buster on the trail, don't just hurry across and breathe a sigh of relief. Practice rock hopping or log crossing a few times, until you become more comfortable with the process. Try it without your pack a couple of times first to gain confidence and stability.
"Sharp turns while going up or down can also be a problem," says Dr. Toole. She advises setting up an S-shaped "turn course" on a hill. Practice by going up and down very slowly. "Exaggerate each step by taking twice or three times as long as normal, as if in slow motion," she advises. "This will put balance at a premium."