Many people like to watch videos of pros. And while this is always fun, it's not always helpful unless you know what you're looking for. And often times new players try to take the cool, fancy, flashy things they see the pros do (e.g. Nony's phoenix build) rather than what they really need to be focusing on. People focus on trying to do that and they don't even have the basics down.
High level players macro first and foremost, they do this so well that people don't even notice it. If you gather nothing else from this, just understand that macro is the most important part of this game. And I don't mean you have to be the macro king IdrA, but you do need to build things on time.
Step one: Pick 1 build. This should be a very basic build that's good against many different things. Don't pick a cheese build, don't pick some heavy micro build. Just something that makes units and attacks like Marine/Marauder/Medivac for Terran, or 3 gate expand for Protoss, or 15 pool 16 hatch roach/hydra for Zerg. I'm not going to get in to the specifics of all these builds. You can find a lot of them on TeamLiquid.net
Step two: Get REALLY REALLY good at doing just that build and only that build. Don't worry about any of the following; scouting, microing, caster units, when to attack, where to attack from, what build to use on what map and against what race, countering, none of that! Just really get your timings down. And by that I mean 5 things.
*Note that you don't want to queue up like 3 units at a time. For example, if you queue up 4 SCVs at once, only one can build and the remaining 3 is 150 minerals sitting around doing nothing. 150 minerals in another barracks!*
Why is this important? Let's take building buildings as an example. If you wait until you have 100 minerals before moving your SCV to the ramp to make a depot, by the time the SCV makes it there you'll have like 130-150 minerals. "Ok big deal? It's 30 minerals" You're right, once isn't a big deal. But what if you build all your buildings like that? After 3 barracks 5 supply depots, a refinery, a bunker, and an engineering bay you're now behind some 300+ minerals. 300 minerals, that's like 6 marines. That's a big deal early on.
The other danger of this is if you don't spend those excess minerals and you end up getting to the point where you saved up like 900 minerals. Then you risk getting in this mind set, "Oh I have 900 minerals. I can make like 5 barracks!!" Then you make 5 barracks, giving you 8 total and you can't even come close to using all of them at once. Now you have several 150 mineral barracks just rotting. That's another 600-750 minerals worth of marines you're missing.
So when do you build more production facilities? When you're making 1 worker, and 1 unit from every other production facility, AND you have enough minerals. So if you're making 1 SCV, 1 marine, 1 marauder and 1 supply depot and you still have 135 minerals; start thinking about making another barracks. Your only goals should be;
Forget about winning or losing. It doesn't matter at this point. And frankly, you're going win your fair share if you're good at the 4 things above. However, keep in mind you will lose for really stupid reasons and you need to be ok with that. I'm telling you not to scout, not to micro, not worry about unit composition. But sometimes they'll attack with a unit comp that just crushes yours. AND THAT'S TOTALLY OK, as long as you did the 4 things above.
This is the basic framework for solid game mechanics. All that fancy stuff like scouting, countering, micro, flanking, etc, etc won't matter if you flat out don't have enough units to make a difference. Sure you scouted his voidray rush, but your 600 minerals that never got converted in to 12 marines aren't going to kill it. Or maybe you killed an extra 4 guys with your fancy micro but that only means he has 24 units rather than 28 when you only have 6. The reason high level players can do things like micro, flank, or drop is because they're making enough units to make those strategies effective. If you can master this, you can easily play at a high gold/low platinum level. Only then should you start looking at those other things that you haven't been focusing on.
Heres a video I uploaded of me using QXC's build order tester to show some of what I was talking about. There are 2 major things to pay attention to:
I selected my larva and was spamming "d" for drone before I had 50 minerals so that when I actually 50 minerals I was making a drone right away. The same thing with the overlord. I also made my queen as soon as my pool was finished. You'll see I had my hatchery selected and my mouse over the spawning pool to see how long it had left, and as it neared completion I start spamming "q" for queen.
I moved my drones to where I wanted the buildings BEFORE I had the minerals, then hit "b" for build and started spamming the hot key for the building while I waited for the minerals.
The little (way way way less important things) that you might notice are:
I split my drones 3 and 3. This give you a little bit more minerals than just sending all 6 to one place, but not something you should worry about.
I set the rally points of the first two eggs individually. First off, some people don't even know you can do that. But more importantly, I set them to the two minerals patches where none of my original 6 drones were.
I went for a creep tumor first. Not only does this help me connect my 2 bases fast, but I also didn't even have the minerals for 7 larva anyway. Why make 4 extra larva when you can't use them?
Drone transfer - In the long run you get more minerals out of this.