grain of salt here Im just getting back in the game after about a 3 year hiatus, but I just placed plat in my placements so heres my opinion:

1) watch your replays, constant worker production. dont have it? get it.

2) build orders. find 1 for each matchup, cheesy or not, but have fun with it. the game is years old, so idk where the skill cap is now on each league, but this got me to plat back in the day.

3) map awareness. If you know where they are, you wont be surprised. take towers, make observers, scout with sentries, etc.

do this, and you can at least hit plat. and if i can do it in placement after only about a dozen games and 3 years off, you can totally get there too.