Immediately when a match begins, go! No time to think, no time to blink, only do. The opening build is vital and demands exactness. Workers, more supply, a refinery: over the course of many matches, you will revise and whittle down these first dozen actions into a masterpiece of design. Even then, are you properly rallying your probes? Is your building placement ideal? There are always ways to improve. And all of it towards a specific object, each a milestone on the path to domination. That tiny edge is all you need to win. And you will need it.
Econ, macro, micro, tech, recon: each skill is essential, and your game is only as good as your lowest common denominator. All potential actions must be considered constantly, and each given due attention. A finely-microed army will decimate an attack-move five days out of seven, though both this knowledge and the requisite reflexes come with practice. A floundering economy will be unable to fund an adequate army, and a poorly optimized economy will waste good resources that, contrarily, your opponent is likely applying. For recon though, there is no substitute. Scouting is unequivocally the most essential and mandatory skill in StarCraft II. Knowledge is power, as they say, a phrase which StarCraft II more than just practices, it requires.
In a recent match, I had finally decided to attack with Protoss ground-forces, and, quite easily, I demolished my opponent's base with little resistance. But something wasn't right; the base had no buildings other than a couple of pylons and refineries. Shifting my army to a fogged expansion, I realized to my horror that my Protoss opponent had not only early-expanded to a high-yield base, but that he'd also constructed his entire base there. My forces were torn apart by an abominable army, and promptly, I was destroyed. But all of this could have been prevented with a little scouting.
Awareness of your opponent's actions at all times is essential. Barring good scouting, you might win regarldess, either by deductive prediction or simply black-mask-blind luck. Let your opponent get the upper hand, though, and you will certainly fail. While you may have a couple of starports reliably constructing banshees, and you're thinking your army is looking pretty good, your opponent may have three hatcheries out there, each with a queen, pumping out dozens of hydralisks every larvae cycle.
Somewhere on the spectrum between plan and reaction, there is a keen balance to be struck. Opening moves should guide you towards an initial or mid-game goal, but you must be willing to adapt to your opponent's strategies, and quickly. Fast-teching to tier three units like colossi or thors may sound like a good idea, but if you don't have the troops to defend yourself and injure your opponent's economy along the way, even a measly enemy force will topple your ill-supportive infrastructure.
StarCraft II is a glorious exercise in the learning process. At my skill-level, upper silver ladder, players are focusing on refining their macro, practicing new micro tricks, and just barely testing the waters of magic-casters. Mostly, we're simply massing two or three unit-types and, on occasion, sending forward a scout. Higher level players, meanwhile, are using magic-casters as a core function of their armies, are constantly aware of their opponent's movements and are frequently raiding mineral lines, and are employing more creative strategies, like baneling drops. These things come with experience. But Blizzard, in my opinion, has done an excellent job with their match-making system, and you'll almost always face opponents who are on the cusp of your skill level, just challenging enough without being impossible.
The races of StarCraft II bear plenty of differences, both in unit make-up and strategy. As well, each race requires a tailored counter-strategy, making for a good number of unique matches (nine, but who's counting?) Terran units are split into three classes: biological, mech, and air. Trying to build all three may make for a diversified, yet anemic, army. Focusing on two classes is generally advised as many units have supporting roles. The medivac can heal biological units, a popular strategy, and hellions can defend close-range assaults on siege tanks. The reaper, a fun, fast unit, can jump cliffs, perfect for raiding gatherers and sniping undefended buildings. Their use, however, is fairly limited beyond this early-game function. Terran has plenty of variety for experimenting with different army builds. And though I've played with them least, I find that they require the greatest macro of all the races, if only because they require significantly more buildings than the other races.
The Protoss are fascinating to play. Their range of units offer excellent diversity and they have plenty of opportunity for creative strategy. Zealots are excellent throughout a game's duration. Immortals are pure beast; they perfectly counter heavy-fire enemies such as siege tanks. Void rays are unquestionably the most cited unit by the StarCraft II community as being over-powered, but they've been balanced out with a number of patches, and their unique (and effective) attack-style and aesthetics are remarkably enjoyable. The stalker, a tier two ground-to-air unit, in my opinion, is the most useful unit in the entire game. And it can blink past enemy base defenses. The Protoss's first spell-caster is also an integral part of a good army and easily the most accessible spell-caster of any in the game.
StarCraft II is the very definition of an addictive game. Losing inspires me to improve, and winning emboldens further victory. Aside from this, the game is simply fun, lots of fun. There are still plenty of balance issues to be found, but the beta ironed out the most heinous, and Blizzard still has a month and a half before the have to pay the dues. Its sad to see the beta go, but on the bright side, I'll hopefully start being a bit more productive with its absence.