Starting Starcraft 2 can be a daunting task, most of the players are experienced from Starcraft 1 and should have no problem, but if you are completely new, I have some tips and tricks to help you succeed.
With all kinds of real time strategy games being around, the most important aspect has always been terrain control. If you can control the map, or at least know what's going on, you're going to have a ton of great success. Once you know what your opponents are doing, the choke points, and other important aspects, you can start winning consecutively. Basically if you have more "knowledge" about the current game, you'll have a bigger chance of defeating your enemies.
Balancing Offence and Defence
Too many people try and make an army straight away without having a lot of resources or having an economy to back it up. Rarely do you win the game with just an army, and if you do win with just an army, it's usually VERY early. You MUST have an economy. Sure, some races are better than others with their economy at certain stages, but you need to have -something- to support you while you fight. Unless it's a really weird situation, usually the person with the most resources will win the game.
Learn the counters to units your opponent makes. For example, marauders hard counter roaches because they deal extra damage.
Starcraft 2 is the greatest game in the world if you are winning, but the worst game if you are losing.
Remember to have fun and with experience, you can get better. Protip: If you've been placed in a bronze to silver league, instead of moving up, just wait for the next league stats reset.
Hope this helped