One issue I ran into was not truly understanding what trees grew in my area. I knew about the big species like oak, maple, ash, elm, you know, the big popular hardwoods. But with a little research I've learned that there is a wealth of others around me such as hophornbeam, buckthorn, serviceberry, black and wild cherry. I had no idea what some of those species were until I started actively researching.
It may seem like common sense, but you need to learn what you've got and how to identify each one. You'll probably be surprised to discover what is growing right around you. Its a lot to learn all at once, so I keep pictures of each species of interest on my cell phone so that I can identify them in the field, or show pictures to those people who could get them for me.