Hey guys. I've been preparing this for quite a while.
This is a bit of a different guide than most, I'm not going to look at any gameplay tips here, because a) I am far from the best person here to be providing those and b) there's plenty already.
What I will do is give a few tips for people stepping STRAIGHT into Starcraft 2, little things, that make a relatively big difference for how easy to do they are, and to stop you from, like me, realising them 2 months down the line and wishing you knew them all along.
1. Turn off mouse acceleration for your mouse. For those who don't know what it is, mouse acceleration is a technique used to move the mouse further the faster you move it. With it on, moving your mouse 1 inch slowly and 1 inch fast will result in different screen travel time. Needless to say, this is bad as it makes your mouse movement unpredictable.
2. As a followup to the above, you will need to crank up your mouse sensitivity, by a LOT, as your mouse will feel slow and cumbersome with acceleration turned off. To give you some idea, my SC2 mouse sensitivity was increased from 30 to 90 when I turned off acceleration.
3. Increase your mouse scroll speed at the same time. While for the majority of the time, you should be moving around the map by double-tapping your hotkeys, scrolling is still necessary and you want to be able to do it fast. Experiment to find the sweet spot.
4. Consider tweaking your graphics settings. While your computer may be able to handle ultra settings, being able to handle it is not the same as having a smooth and consistent framerate, and smoothness is critical. That said, if your computer can handle it, using low or high settings is a preference thing only and those who say it makes it easier to see things on low settings are just being silly.
5. Have your Health Bars set to Always shown. This is important to know which enemy units are hurt worse so that you can focus fire on them, and conversely, when you begin to learn how to micromanage your units better, to retreat your own wounded units.
Beginning your first games
1. Skip the practice league. It teaches you nothing, games are played on a much slower speed, even a monkey could play a perfect game at that speed. You also have rocks protecting your front door, which can't be destroyed easily. While this seems like it'd be good to protect you from early rushes while you learn the game, what it actually does is promotes high-tech strategies, such as rushing for air units, strategies that will get you killed in normal games. You learn nothing from the practice league. If you need time to figure out what buildings do what, play the campaign (if your race has campaign missions at the time of reading this) or play some games vs Very Easy or Easy AI.
2. Don't stress about losing your placement matches. If you do your best in them and lose four or five of them, you will most likely be placed in the bronze league. Don't despair! This is a good place to be if you struggled with your placement matches! You will not be facing amazing idiot savant gamers with 500,000 APM and perfect knowledge of every build order in the game when you're in Bronze. You will most likely be facing a lot of people just like yourself, and you will win as many games as you lose.
3. Save your losing replays. Look at them later. See if you can figure out what you've done wrong. There are numerous guides out there that tell you what you should be doing. Applying them to your game is the hard part, but you should be able to soak up a lot of knowledge, even if you can't necessarily apply it to your gameplay yet. Everyone is the world's best Starcraft 2 player when they're watching themselves or someone else play, you will be amazed how easily you spot mistakes you didn't even notice in game.
4. Ask for help! Penny Arcade has a thriving Starcraft 2 community, and frequently people post replays in the threads for advice, critique, and sometimes just to show off a particularly fun or exciting game. Use the resource! the most common site used for replays is www.gamereplays.org
You will notice that, in some of your games, perhaps, at the beginning of the match your opponent might say something like "gl hf" or "gl gl". This means, in essence, "good luck, have fun". When the game is over, the loser, when they decide they've been beaten, rather than simply opening the menu and leaving the game, will sometimes say "gg", and if they want to be extra nice, "gg wp", which means "good game, well played". While some scoff at this, I find it is a good practice to adopt. Quite apart from being respectful to the human being on the other end of the computer (Sometimes people forget this, I know I sure do), it also makes you feel better yourself. When I lose a game and just quit right out of it (called rage-quitting, sometimes), I feel awful about the loss. I get angry and I sometimes just stop playing for the night. However, in the same sort of loss, when I bite back the anger, relax, and say "gg" to my opponent, I feel inexplicably better about the loss. It feels more like a friendly match between good friends rather than an intense competition between strangers.
This is especially true if you lose to something sneaky like a Photon Cannon rush! Resist the temptation to swear and scream at your opponent (feel free to do it in real life of course!). For someone who enjoys sneaky tactics for the cheap wins, getting angry only makes them happier, you will deny them the satisfaction if you remain respectful. And for those who are simply using those strategies because they think they are a fun way to play and win, being respectful is just good manners.
That's about all the very early beginner tips I have. Remember, Starcraft 2 is a game about losing as much as it is about winning, and while winning is obviously more fun, losing can be fun too if you are gracious about it and if you learn from it! Don't get too disheartened when you lose, and if you lose a few games in a row and are getting frustrated, take a break! play a different game, or try some Custom games, analyze one of your replays and see if you can learn what to do better next time, or even watch a pro-level match on Youtube or something similar!
Go out there and have fun!