Haha, I was really hoping to get that cast out today, but looks like I have to keep studying. Gotta truck on through those midterms. Here are some tips instead to give you guys something to think about.
-Building on what I said before, use the early overseer to stop early rushes like void rays or colossi with its contaminate ability. When utilized properly, important game changing units can be easily stopped in their tracks until it is too late. When using a zerg infantry for example, look out for factories pumping out tanks or robos pumping out colossi.
-Don't forget about thinking about an early phoenix. Early phoenixes can lead to great harass and scouting as well as picking off any air units before they become a serious threat. They are excellent in later game for picking up tanks or immortals, rendering them useless.
-Don't overlook the hellion. It's a very successful harassment unit in all stages of the game. If you can sneak past armies or defenses, the worker line gets blasted easily, especially with the upgrade!