Get some minimal gear, hit the woods, and climb
Move around from place to place in the trees, walk limbs, tarzan a little, and just get comfortable with equipment. You do not need to be working for a tree service to learn to be an expert climber. When your climbing skills are good, start taking your firewood trees down from the top, using saws, ropes and tackle as needed.
I started tree work as a groundie, but was already a better climber than anyone on the crew, but I learned alot about cutting limbs watching the experienced climbers. I still go to the woods to try new(to me) tricks and equipment.