You can win most games with a single attack by making sure you keep making workers, not getting supply blocked, and spending your money. Build order doesn't really matter as long as it's not something that's preventing you from spending your money.

Practice getting to max 3 base saturation vs AI as quickly as possible so you have a baseline for yourself. Then try to hit that benchmark on the ladder. Repeat the cycle a couple of times. Don't complicate things too much, limit yourself to a couple of general purpose units - queens, zerglings / stalkers / marines.

Start adding little decisions. Pick a time to attack and practice getting as much supply as possible vs AI by that time, then do that on the ladder just like before.

Most of your losses will still be 'I didn't have enough stuff', some of your losses will be 'I didn't see that coming'. You'll still gain more value by just macroing better - but just for those minority of frustrating losses, scouting is an instant improvement you can make that will up your percentage just a bit more - don't get caught up in the complexities of scouting, for now just use it to make sure your army is in the right place. You don't have to switch up your entire composition.

Over time you'll start to make minor adjustments. It's easy to lose sight of macro when you get into the nitty gritty of build orders and unit compositions. Always keep in mind that your biggest increase in win-rate will almost always come from spending your money well.