In order of decending important, you should be thinking about the following things:
1. Always be Doing Something.
As I see it, there's only ever three things to be done: Attacking, expanding, and teching. If you're not doing one of the three, you're doing nothing. I see this a lot in low level replays; people tech quick to Lurkers and then sit at home with them. They don't go Hive, they don't expand and they don't try to break their opponents expansion - they do nothing.
By the same logic, a containment is doing you no good if nothing is going on beyond that containment. If you're not holding up for more expansions or more tech, that containment is pointless.
You should note that Teching means teching NOW, not in 5 minutes. If you're "going to be" teching, you're still not doing anything.
There are two times that I can think of when this wouldn't apply. Those are the time when you are building up for an attack, and once the late game kicks in and resources are getting low.
Try to think about this during the game. Make sure you're always doing something.
2. What's your underlying game plan?
It's ZvT. Instead of powering Drones off of 3 Hatcheries, you got Lurkers quickly off 2 Hatcheries. Now what? Why would you use this build? Either to break his natural, or secure more expansions for yourself. It doesn't make sense now to add many Hatcheries and get many Zerglings. If that was your plan you should have added the Hatcheries before Lair.
This happens all the time to one of my friends. He's good, but whenever I watch a replay he needs help with, I ask him "Why'd you do that?" and "What's your gameplan?". He can never answer. You should be able to watch your own replays and be able to explain your plan to yourself.
Now that you stole build orders from replays to satisfy #2, it's time to adapt. In ZvT, it's 3 base (2 gas) Zerg versus 2 base (2 gas) Terran. You were planning on going Hydralurk until you scouted Terran with 6 Barracks and 2 Factories. You're going to make life easier if you switch to Lurkerling.
Sometimes you have to use Ultras. Sometimes it makes more sense to use Defilers. Sometimes it makes more sense to use both. Sometimes you don't need Hive tech (rare). If you feel Terran is going fast Tanks and you just stick with your 3 Sunkens and Spire, you deserve to lose because you didn't adapt.
So, have your general cookie cutter builds, but you have to stray from them when you see Terran went 1 Vulture into 2 Port Wraith, or basically an unorthodox build.
Sorry all my examples are ZvT just because I have that on my mind for some reason.
4. Macro & Micro
Now that you've done 1-3, you should start worrying about macro and micro. I see a lot of people starting with macro when people ask for help. I think it's much more important to be "always doing something" than having good macro, that's why I put these so far down the list.
So, if you watch your replay and you think you did all 1-4, then ask for help. I can pretty much guarentee that if you are always doing something, following a game plan, and adapting your build to counter his, you won't have a replay that you still need help with.