Plant Amnesty has a great book and website that details the proper way to maintain and prune plants and trees. Check out their website for a wealth of information. It's important to know what to look for in a tree service person's skills so that your yard won't grow back to haunt you. I learned a great deal from their materials and I'm glad because there are a lot of yard services out there that will happily take a chainsaw to shape a tree or bush. Check out their plant Hall of Shame - it's funny but more so, it's sad to see what people do to their plants.