Back to basics?

I set up a list of small things to check that are ok.

Building placement:
Do units get stuck behind or between structures? How to avoid this?
How does your building placement act towards you and attacker when you are defending drops?
How do your buildings increase your base awareness?
Supporting mechanics: How do you perform building placement? How could it be more efficient?

Macro:
Nonstop worker production. Should the unit production also be nonstop or reactive? From robo and stargates maybe nonstop but from gates? Did you have too many or too few units? Why were there too much or too few?
Supporting mechanics: Checking probe & unit production frequently enough.

Expanding:
when ever you have enough units to defend your expansion and have enough money to build one. So basically? How much does he have units? Is he going to attack? Did you have enough units, too few units or too many units? Did you expand when you could have unit and money wise done so? When did these suitable spots occur? Did you make additional unit production facilities before you expanded?

Initial scouting:
How well did you control you probe? What do you want to find out? When can you leave and why? Did you probe die? Was your macro affected? How do pros perform this initial scout?

Keeping Xelnaga towers:
What are the benefits you find?

Army positioning:
Are you grabbing the best defensive advantage? How could you have more defensive advantage?

Teching:
Gass means going down the tech tree. When can you afford to start collecting gass or using it for tech? Haha, what if you just take gass very greedily like before some important first buildings? What can this lead to?
Does optimal teching mean that you place the tech as you have enough gass? So does optimizing a build mean that at that moment you will have enough minerals also?
Did you advance through the tech tree? Where did you stop? Why? How smooth was this advancement? Maybe make a plan how to tech through the whole three? What are the rock, paper and scissors? The amount of units might change its rock, paper, scissors status?

Upgrades:
Did you keep them strolling? Were you ahead or behind your opponent? Why did you not built forge earlier?

An incoming attack:
Did you see the attack coming? Why you did or did not? Did you know what upgrades, what composition and what unit count? What was your reaction? Was this the best solution or could something have been done otherwise?

...
seems that the list became quite long :p. Maybe just pick few things and check that you are improving on those. Or make it like a game: 1st 1 thing, then 2 things, then 3. etc. See if you can go over the limit of human mind (4-7).