1) There are only a few hard and fast rules that I can think of.
Some are:
don't start ACU upgrades that you can't afford. RAS in minute 3 is usually a FAIL
don't forget to scout
don't forget to build an energy storage so you can overcharge
don't forget to scout
don't overbuild energy early on
don't forget to scout
don't upgrade too many mexes at once
don't forget to scout
2) Watch replays of wins and losses - try to identify your mistakes and correct them
3) Watch casts, learn from pros who cast and from Gyle. It's like a free education
4) Start with known good build orders and adapt them after you have them down
5) Learn the maps - not knowing where the reclaim is usually means a loss if your opponent does know where it is
5a) Practice against an ai on maps that you suck on. Figure out why you suck on that map in particular.
6) Avoid the temptation for a cheese win until you know you have no other option
7) Chat with those who have just beaten you to see if they will offer up suggestions, most folks here are good people
8) Learn what mods are popular and get them. You are at a disadvantage if your opponent does and you don't. It sucks, but it's true.
9) Listen to teammates advice in game, they may know more than you do
10) Stop making the same mistakes over and over.
11) Ask questions in aeoleous and the forums. FAF'ers like to help each other
12) A draw is better than a loss - take the other guy down with you if you can
13) Mass in storage is (usually) a very bad idea - spend it if you got it, if you can't spend it, try to upgrade something
13a) Never let mass overflow - you can't get it back.
14) Encourage newer players. we need more people playing.
15) Learn what to use to counter your opponent. Put it on notecards if you have to. It's easy to freeze up in game. Take a deep breath and think it out.
16) Build templates are your friend.
17) Remember to keep growing your eco.
I'm in the process of learning to do all these things myself.