Too often, new players are content to sit in his or her base, only to be completely caught off guard by their opponent's army. To combat this, you'll need to scout your opponent as often as possible. What is most important, however, is to understand what your opponent is doing based upon what you see and correctly alter your play to counter what you see. Similarly, denying your opponent scouting information can give you an advantage.
You should start off with sending an early worker to your opponents base and keep it alive as long as possible. Any harassment you can do to get your opponent to pull workers off of minerals is a bonus, but don't sacrifice your own base-building for keeping your scout alive. If need be, just send your scout away and send it back in 30 seconds later. After that, each race has its own methods of scouting, discussed below:
- Terran: Scanner Sweep on Orbital Command - Exchange 50 energy on the Orbital Command to reveal a section of the map temporarily. This should be used sparingly as that same energy can be used for MULEs, which help your economy. The Scanner Sweep will also reveal cloaked units like Dark Templars, Banshees, or burrowed Zerg units and should be saved if you suspect an attack from them.
- Protoss: Observers from the Robotics Bay - Protoss players should generally get a Robotics Bay for Observers, which will also reveal cloaked units. Your first Observer should be sent directly to your opponents base with additional ones added to follow your army and hang out at your minerals if you fear cloaked harassment.
- Zerg: Overlords, Overseers, and Changelings - The initial Overlord should be sent to the closest starting position, while the scouting Drone should check the other bases. Eventually, Zerg players will be able to make Overseers, which can spawn Changelings, and speed up their Overlords. If you need a clear picture of what your opponent is doing, just send one of these to the enemy base. If you can get a Changeling in, do so, as many players will overlook them and you'll get constant scouting information.
- Proxy Rush (Terran, Protoss) - If you don't see any Barracks or Gateways in your opponents base, it's likely that they are doing a proxy rush, meaning that they are building their army close to your base to minimize travel time for newly trained units. It is generally an all-in strategy.
- Fast Reaper Harass (Terran) - Reapers are an effective unit for economy harassment early on. Tell-tale signs include the Terran opponent getting 1-2 gas Refineries early and adding a Tech Lab to the first Barracks before you see any Marines (some players may get 1 Marine).
- Zergling Rush (Zerg) - If your opponent's Spawning Pool is finished or nearly done when your scout arrives, prepare for a Zergling rush. If it is already finished, count the number of hatching eggs to estimate the number of incoming Zerlings. Remember, there are two to each egg.
nope One of the most difficult things in StarCraft is knowing when the expand to a new set of minerals and gas. Most new players will never expand, but will rarely survive long enough to have this matter against a skilled player. As you improve, you will need to start taking expansions and securing economic advantages.
In general, unless you are doing a specific build that is designed to execute a fast-expand, either with containment of the enemy or a defensive wall-in outside of your main base, you'll want to expand after you have a significant skirmish victory. Did you decimate their army leaving them on the ropes without taking too many losses? Instead of committing those few units to an attempt at killing him entirely, use the momentum to take an expansion. By doing so, you place yourself at a much bigger advantage for the long-term. If you attack, you could do some damage, but if you are repelled, you might lose that advantage.
Deciding between going for the kill or expanding will always be situational, but the safer play will usually be securing the advantage. A better economy means that you can produce more units, tech up, and reinforce an attack much more easily than your opponent. Zerg players will want to try and secure their natural expansion--the closest set of minerals to their starting position--as additional Hatcheries create more larvae for unit production.
Also, since you've been creating workers non-stop, you should have more than you need at your main base. Transfer a nice chunk from your main to your expansion when it finishes building to immediately increase your economy.
Finally, multitasking, even at a base level, can lead to victory over a similarly skilled opponent. Use your hotkeys and do as much as you can without moving the camera back to your base to create units. Your Command Center/Nexus/Hatchery should be hotkeyed for quick worker production. Similarly, your unit production buildings should be hotkeyed to create reinforcements during an attack or defense.
During a battle, you generally do not need to micromanage every little movement. When you see a moment of freedom, queue up some more units using hotkeys and then start controlling your army again. By carefully setting rally points, you can ensure that a steady stream of reinforcements will join the battle as it goes on. If your opponent isn't doing the same, you'll most likely end up overwhelming them.
Protoss players will want to create a Pylon close to the enemy base so additional units can be warped in. It requires a bit more attention, but hotkey that Pylon so you can immediately focus the camera on the powered zone to warp in troops.
Try to work these tactics into your game, but don't sacrifice the basics discussed in part 1 to do so!