Take a comfortable fold up chair, and sit for at least 10 to 15 minutes at a time.
I have timed it, and they will start moving between 7 and 12 minutes.
Bring some 6x binoculars; they will hide in the strangest spots.
Like on a limb fork, or lay flat on the trunk.
Take a small round mirror, and when you see a squirrel go in a hole, reflect the sun into the hole, be ready to shoot they don't like the light shining on them and will come out.
Just be patient, take your time.
Good Luck.