In order to improve your skill and dominate other players you need to learn such concepts as scouting, macro, and micro.
Scouting is important because you need to read what your opponent is doing. You can do this with a worker at around 10 supply count but then you need to scout again to see what units he is going for so you will know what to do next.
This is when you should be using a technique based on the race you are playing as. Zerg can scout with their overlords by sending over two or three to kind of surround their opponent and occasional come in to spy on them.
Terran can do this by training a reaper to hop up into their base and look around before getting killed. Or they can send in a hellion if they are going for a mechanical build.
Protoss has the best scouters in the game which are observers. Send on over if you are going for an early robotics facility. If a 4 gate build then you can research hallucination for sentries and send a fake phoenix to fly around their base for a good read.
Then there is macro and micro. Macro refers to building your economy, unit production, and building structures while micro refers to controlling your army in battle to make them most effective.
To build a rich economy you need to keep producing workers and then expand at the right time according to what your opponent is doing. For proper micro you need to practice using special units like ghosts, sentries, and infestors. It takes lots of practice but eventually you will get it down.