I'm on same boat as you, although I have started playing on ICCup. I suppose it's about making best use of hotkeys. You'll need to maximize two things: mineral/gas mining and troop training. If you've managed to get that far you must learn to use hotkeys for effective grouping.
I have no idea how many people seem to do it so effortlessly. I get beaten by computer in skirmish no matter how fast I try to click.