StarCraft 2

Shared Control
Shared control is an often overlooked feature of 2v2. While its biggest use is when one player gets double teamed early on and taken out, after which his ally gives him shared control to even up the micro battle, it is also useful to enable when one player is harassing with Mutalisks or Banshees so that the other player can have control of the main army for a simultaneous attack or to defend a counter attack while they can have their whole attention on microing the harass.

Unit Composition
It’s perfectly acceptable in 2v2 to leave a hole in your unit composition that you wouldn’t in 1v1. If one player has, say, mass Blink Stalker then the other player doesn’t need a large amount of anti-air. Complementary unit mixes are an important part of 2v2, particularly with early aggression. One of the most common openings is to combine a ranged unit with a melee unit, such as Zerglings and Stalkers or Zealots and Marauders. Later in the game you still need to make sure your armies are complementary, an army mainly composed of Roaches and Marauders isn’t going to be as versatile as say Roaches and Marines. It’s also worth noting the abilities that can be used to help your partners’ units, particularly as Terran. Immortals with SCVs on auto-repair are devastating and a crowd of Mutalisks being followed by Medivacs is a scary prospect.

2v1
In a lot of games, especially on some of the maps with individual ramps, it’s common for one player to get double teamed early. The player who dies or nearly dies to this early push still has an important part to play in the game. It’s generally a good idea for the strong player to give control to the weaker player to make sure the micro battle is still on an even footing. Unless the weaker player got taken out extremely quickly it’s likely that his strong ally will be ahead of both opposing players combined and with shared control the game becomes as it was before, except the team that took the early hit now has an advantage. It can be a good idea for the weak player to funnel gas to his ally allowing him to produce high tech units quickly or get mass upgrades to maximise his lead.

Scouting
The main obvious difference in 2v2 is that there is twice as much to scout. However, once you’ve scouted one player then both you and your ally have that information. It’s also possible to make a good guess at what both opposing players are going for with your early scout by seeing just one base, although you shouldn’t rely on this too much. Scout a Terran and see no gas, two or three Barracks and no Marines? Then he and his ally are going to push you very quickly. Or is the Terran making a wall in between his ramp and his partners’ ramp? If so they’re teching hard. Scout the other player too, but that piece of information from the first base can inform your build enough to start preparing immediately. With third bases being so difficult to hold in 2v2 it’s vital in the midgame to have as much visibility of the expansion locations as possible in order to deny your opponents a third base. Keep scouting their mains as teams often look to mass two or three specific units, so scouting a turtling and teching team at around the eight minute mark by scanning or using an Observer or even sacrificing an Overlord can make it very easy to prepare for what they have and get the correct unit mix.