7. The Importance of Scouting

Playing a lot of melee custom games, a common mistake I see amongst newer players is the lack of scouting they employ throughout the game. I wanted to go through some basics methods for scouting as each of the 3 races. It is extremely important that you scout and be aware of what your opponent is planning to do and respond accordingly. Games at the highest level of play are often won/lost due to insufficient scouting and/or map awareness.

Initial Scout- All Races
Around 9-12 supply you should almost always send a worker (SCV, Drone, Probe) to go scout your opponents base to get a basic feel of what's going on. This is very helpful in determining what you will build depending on what information you gather. Usually you want to keep your worker shift+moving around the base in a circular motion as long as possible. Against Protoss you can keep it in there before the first Stalker comes out. Against Zerg, try to get your worker out before the first zerglings are out. Against Terran you can usually keep him there until the first marine is out. After the initial scout I usually take my worker to one of the Xel'Naga watch towers for some recon. Even after the initial scout, you could always risk sacrificing a worker to poke around your opponents base and see what's going on. It's often worth it, especially versus Zerg due to it being damn near impossible to wall off early game. Most Terran and Protoss players seem to have an easier time denying this method however.

What to make of your initial scout- When you keep playing, you will notice patterns occur when your opponents are going certain builds. For example if by the time you get to your Z opponents base, his spawning pool is already done and he has 3 eggs morphing in, 9/10 times he built his spawning pool before 10 and is now going to be rallying those 6 zerglings to the front of your base. If your T opponent has 2 gas up and is throwing down a reactor, be ready for Reapers, Banshees (or Both) , quick Tanks etc. If your P opponent has built 2 gateways and is chronoboosting his initial one as soon as it spawns, get ready for 2-gate pressure. I think the best advice is to just pay attention to what your opponent is getting and where he places his buildings and then see what comes out of it. Also go to Teamliquid.net and check out the 'Liquipedia' build orders and familiarize yourself with them. As you keep playing you will start to see patterns in the build orders. 

Protoss
I feel like Protoss has less early-mid game scouting options than the other 2 races. Terrans have scan and delayed reapers, Zerg have Overlord spotting and Zergling mobility on their side, Protoss can Hallucinate a Phoenix, but it takes a while to research so by the time it comes up because you would almost always want to get it after warpgate.. You should have observers around the same time. Once Protoss have observers, I feel it more than makes up for their lack of early game scouting options. Often when I play PvT I poke up his ramp with my army to see what I can see. You can tell a lot by what units he has already. For example, if he has a bunch of Marauders and a couple of marines, he may be going a 3rax timing push with stim and concusive shells. This composition might be vulnerable to voidray harass. If he has a few marines and a factory coming up, he could be going 1/1/1 build or be going a MM+Tank build. etc. It's dangerous poking your army up a ramp in PvP because of Forcefields. PvP has often been described of having a Roshambo type quality due to the fact that in many cases if a player goes for a quick observer to scout, he can sometimes be overpowered by a 4gate build. If a player goes 4 gate, he gets countered by a Dark Templar build etc. I think this is due to a lack of early scouting options on both sides. PvZ I like to hide my probe somewhere outside their base after the initial scout and run in maybe a minute or 2 later to see whats going on, a lot of zergs place their armys at the top of the ramp, but many times they are being active with their army.. doing things like harassing, destroying destructable rocks etc. Again once you get your observer out it becomes pretty easy to see what your opponent is up to and where his army is.

Terran
To me, Terran has a lot of early-mid game options in terms of scouting. My favorite is the semi-delayed reaper. It works pretty well in all matchups and on most maps. All you have to do is just skip one in your normal build order and instead make a sacrificial reaper to run circles around the opponents base and maybe earn his keep by killing a few enemy workers in the process. It's important however that you remember that the primary function of this 'delayed reaper' is to gather intel, not worker kills. As the game goes on however, and especially if you keep sending reapers to scout his base, A good player will start to deny these scouts. Scan is also a very viable option for scouting, however I have heard that one Mule mines ~300 minerals in its lifetime so in many cases I'd rather sacrifice a Reaper (50/50) to get the job done instead. Also it's sometimes nice to save a scan for emergencies, for instance if your P enemy hid his DT tech somewhere ridiculous like at the corner of a 4 player map. Another great and underutilized method of scouting is the Sensor Tower. The Sensor Tower reveals enemy movement in a pretty large area, it's especially useful If you're going for Siege Tanks because it prevents you from getting caught out of siege mode or out of position.

Zerg
Early-Mid game one of the great things you can do with Zerg is place overlord 'spotters' on high ground to detect enemy movement or incoming proxy (buildings built in close 'proximity' to your base) cheese. Zerglings are also great sacrificial scouts, costing 50 minerals for 2 of them and moving slightly faster than probes. Many good players place their first 2 or so Zerglings at Xel'naga watch towers asap and often catch their opponents workers there. Good Zerg players will also sacrifice an Overlord to get a good idea of what the enemy is doing before he has an Overseer. Once you do have an Overseer, they make excellent scouts (especially with the speed upgrade. You can also spawn changelings which turn into an enemy Zealot , Marine or Zergling depending on the opponents race and have it follow his army around. In addition to all these options, A Zerg player can see wherever his creep is, so a defining feature of many pro Zerg players is constant spreading of creep 'highway' in all directions.