Time for Mojos big giant post of slightly useful info! This will be a collection of things I have learned while toying with sc2, as well as learned via replays/shoutcasts and so on.
Random infos: Time units for building/research are in seconds, however the number is assigned as if you are playing on normal speed. As the game defaults to faster, the actual time to build is less than the listed.
2v2 games, you can share unit control. This can allow one player to focus on macro and economy, the other microing the army.
Main stuff:
First and foremost for being better at sc2 is getting the macro/micro down. Learning and memorizing hotkeys to build units/structures is paramount. In addition to this, hotkeying your production centers so you can produce units while on the far side of the map without zooming back is another must. Having all your 'Rax assigned to say control group 4, lets you work on a battle, hit 4 a single time and begin queuing reinforcements. This also allows you to ensure you do not have an unnecessary stockpile of minerals. If you cannot burn minerals fast enough, you do not have enough Rax/hatch/gateways/etc. I have watched duration matches in unofficial tourneys where a player will have 8+ rax/gateways/etc. The obvious exception to this would be having 6 or so bases to the opponents 3. Stockpiling some is going to happen at this point.
Also with hotkeying, is timing the use of your command center/nexus/queen abilities. Mule are worth 270 minerals if deployed on the patch, they can also repair units in oh shit moments. Weigh that vs the scan to scout. The supply thing is pretty much ass, do not bother, use a MULE instead. Queens of course primary ability is +4 larva every 40s (normal game speed), followed closely by creep tumor (more on this wonderful things later) and a small heal which can be useful to keep spine crawlers alive and what not. Lastly is chrono boost, this one is all kinds of fun to play with with it improving the speed at which a building researches/builds things.
Some examples could be. Terran flys a CC over to a gold patch, while scv production takes a min to get going, you could drop a MULE on each patch provided you had the energy. This provides a massive boost to your economy while scv are relocating or building.
Toss, you can chrono boost the nexus for quick probe production, or save it for first gateway to kick out a very early zealot, one that could demolish a fast expand build opponent if they did not scout the chrono being saved rather than used on nexus.
Zerg is pretty simple, 19 larva max, so the primary ability to be used will be spawn larva. However, kicking out a creep tumor or two is highly advisable, do so when you have several larva spare and are not building any units currently.
Scouting: Oh so very important. Your initial build is very important, and must be changed up depending on opponent race (should they play random). After that you need to asses if they are going early aggressive, fast expand, quick tech and/or focusing on certain units. A zerg player for example should be wary if they see a factory with a reactor and must gear unit production toward dealing with hellions, spine crawlers are also very useful for dealing with them. Scouting with an scv/probe is typical. As for when to send on, below is a chart showing mineral loss based on which worker you send. The key is to get one early enough to get in before the base is walled off (toss/terran) while doing as minimal damage to your economy.
Lets say you got your worker inside a terran base, the terran is currently working on the choke point wall. If you can, target the scv constructing the rax/depot (not the building however) and use your worker to attack and try to kill it. If successful you just cost your opponent 50 min, and time spent not only rebuilding the worker, but time lost on the building being constructed. If this is not an option, shift click to set waypoints for your worker to make the rounds in the enemy base, be sure to check behind the mineral patch for hidden buildings. You can also try building on their gas to slow them down if they are fast teching and want both geysers (this is more for zerg and cheap extractors). Ultimately you want to keep your worker alive as long as possible (if trapped) and keep an eye on buildings/units being constructed, if chrono boost is being saved etc. Else, after a few laps and enough info is gathered to adjust your build order, evac the worker back to base, or camp it near for a proxy base/etc. Continue to scout your enemy from time to time and make adjustments to your unit composition as needed.
Build orders and how to understand them.
Any idea what 14 pool means? 10 pool? Overpool? Depending if SC is new for you, probably not. So here is how this works. The number is associated with the current food/population count. While the word is the action at the given point. 14 pool for example means once you build your 14th worker, you construct your spawning pool. Overpool means building the overlord at 10(11 min, more on this trick later) and as it finishes the pool is built. The format will be the same for all races with the structure being different obviously.
A lot of your time will be spent learning and memorizing the current primary builds for your fav race, as well as how to adjust them based on opponent and what build they are going. Your early build is very, very important and should become very natural for you to proceed through each game.
General tips.
It takes 3 workers to fully saturate a given mineral patch or geyser. Fully saturating a mineral field however is rare, though having it heavily covered is the best route.
Workers in the mineral fields will automatically move to unused patches, this is true for your initial 6 workers. General high end players select all 6 and direct them to one end of field, quickly drag selecting 3 and moving em to other end, this allows them to spread out quicker. Setting your worker rally point to mineral field will cause all built workers to start auto mining, this saves some time.
Capitalize on distractions. If you are crushing an opponents expansion, quickly build another expansion of your own. Losing an expansion? Drop in the enemies base or hit one of their expansion. Both armies engaging in center of map? Sneak some burrowed roaches past the entrance and get ready to demolish workers. Use the xelnaga towers, check in weed/smoke areas as well as up ramps for proxy pylons that might be used for warp gates.
Toss tips.
Toss cannot initial block their choke like terran due to no lowering buildings. Zealots on hold ground work perfect for blocking the entrance however. Sentries do very solid damage in addition to their powerful support abilities. A few sentries microd can forcefield a small ramp for some time to prevent attacks. Double pylon primary construction clusters, otherwise a few banelings/reapers can ruin your day. Colossus can be hit by air to air units, while not being able to attack them back, keep this in mind if the enemy has a lot of air units like vikings etc, reconsider constructing colossus. Warp gates rule, place a proxy pylon in some smoke/weed areas or up a ramp so ground units running by will not see it. Warp units from gates in and reinforce forward army faster.
Terran stuffs.
Basic walls consisting of supply depot or a rax+ addon can be very dangerous against zerg. A handful of banelings can demolish those smaller buildings allowing speedlings access to your base and your worker line. Reapers can hop up and down cliffs, and 3 of them will insta pop a worker great early harassment. If you see a baneling nest, rethink your M&M build, it will not last long if the zerg player is using a decent amount of banes. Nuking a mineral field is horribly effective, even if your opponent moves all the workers, the minerals lost by not mining will most certainly be far more than the nuke cost. Ghosts hurt, a lot, and not just with emp and nuke, however emp + nuke against toss = lulz.
Zerg.
Extractor trick: get 10/10, send drone to build extractor (25min), make drone with free food slot, cancel extractor, celebrate you are at 11/10. Creep is amazing, it acts as a scout letting you see the area it covers, it helps your units regen, and best of all it improves the speed of your units, by a lot. Using overlords to spread creep as well as creep tumors gives you a speed advantage against opponents. Spread creep, lots and lots o creep! Overlords are no longer detectors, you must upgrade them for that, but do not upgrade all of em, spawn creep owns! Changlings do not do anything beyond take the shape of nearest enemy, this however is good because enemy might not realize what they are unless they target the unit, and they provide you with scouting and LoS for worms. Nydus worms do not require creep to spawn on, they can spawn anywhere you have LoS, though they take a few seconds. This allows you to hit the enemy worker packs if you can get LoS via overlord/changling.
More crap later.