There's nothing more important to success in a real-time strategy game than understanding exactly how the tech trees are built, so you can figure out when and how to make which unit. Since you can't get started learning too early, Blizzard has provided the current tech trees for all three factions in StarCraft II.
Grab the full high-res versions over in the StarCraft II image gallery, and keep in mind these are subject to change during the beta.