Go to your local library. Figure out where their field guides are. Check out a couple tree books. If they have some that are specific to your region/state, grab those.
Flip through them over the next few weeks. Learn the trees in your back yard. The next time you go for a hike in the woods, identify as many trees as you can. If there are books that you find especially useful, consider buying them.
Eventually, you won't need the book anymore.
These days I rarely come across a tree I don't know, and when I do it's usually an exotic ornamental or a non-native species. Put me into a different environment and I'm kind of lost, but not clueless. Most of the time it doesn't matter if leaves are present or not. *Some* species I can identify just by the wood, even without bark.
How did I learn?
Basically using the method I described.