Heading back a tree is cutting its canopy branches back to the nodes, or growing points. Thinning a tree is removing a small number of branches back to the trunk. The earlier you make pruning decisions, the better. Envision the tree in a year, or in five years. Finally, decide if the tree needs to be lifted.
Most trees look better when lifted.
I like to see a tree with a trunk, not a thirty foot shrub. To lift the canopy, remove the lowest tree limbs all the way to the trunk. Make your cuts correctly. Leave the branch collar on the tree, and never remove more than 30 percent of the foliage. You won't need to use pruning paint if you make your pruning cuts correctly.