You need to learn build orders and mid game strategies. There are many professional teams and commentators with nice sites and tips. Team liquid have a very good forum and Blizzardhusky(Or is his name starcrafthusky) commentates on Starcraft matches. He provides amazing insights if you can put up with the fact he treats it like a Spanish football match. There are a few wikis and such but once you learn your build orders it's trial and error to learn what opponents do and what seeing certain things in their base means. Took me a good 20 losses in a row to realize that I had to scout out Terran expos and get rid of them fast.
There is no one great tactic and you learn to play in stages, first your early game will get good, then your mid game, then your late game (It's really tough once your minerals start going low) keep at it though, Starcraft is a game I only discovered with the Beta but damn do I love it.