Overall in the 2v2 environment you ideally want all your units gathered as fast as possible mainly because all those defences in 1v1 are less effective when you encounter higher supply armies. Things like forcefielding ramps or using spine
defences are effective on a duel because they will provide you an economic or
technological advantage over your opponent later on. But in 2v2 and especially on a
map with a non mutual choke point early aggression will most likely kill you. Think of it this way. If you plan for a 14pool, which is economic and standar and your opponent 6pools you, you might loose 3-4 drones defending but you'll still be ahead. Same if he 9reapers you. But what if you get 6pool and 9reaper simultaneously? You die to that.
So speaking about early aggression there are usually two major time marks, the 4th minute and the 7th minute mark. At the 7th minute you are usually called to face a big one base all-in push that you can only defend with about the same size of army. Does this mean the game is a bit boring and repeatitive? Perhaps. Does it differ from 1v1? No. Or at least not dramatically. In 1v1 you get more defensive options over a small variety of units combination depending on the matchup. What you need to have is good communication, good unit combination and ofcourse coordination. You will be most likely in a situation where you and your opponent share the same macro so unit micro and position will be the decided factors.
There are certain builds that can guarantee you a smooth transition to the mid game. Consider the early game being a bit "extended". Those early battles can decide at best who gets the advantage or even decide win or loss. You can usually go bio-ling or bio-ling/baneling (if you are facing another zerg who is massing lings too) or just marine-ling or marauder-ling depending on your plan over you opponents. Building roaches is a double-edge. You have a strong but immobile army that is slow to build (cause it takes more than the standar 15 drones to mass those and then your opponent may tech to spire). Playing terran-zerg and especially passed the mid game you should keep in mind that the zerg should provide the mobillity and the map control while the terran provides the heavy artillery. Zerg having the mobile army should always be able to harass or counter-attack.
Micro-wise you should always keep in mind that you don't wanna loose your zerglings; small packs of lings are no good while big packs are deadly. If the battle involves baneling micro you are ideally want your ally to focus the banelings or you should sneak a single or a pair of lings to get them detonated (if your opponent is not controlling them at that point). If you face a mirror, mass marines are favored over marauders but if you face a PZ combo marauders are obviously really good against stalkers. The basic idea is to have your banelings protecting your ally's ball and not really trying to snipe your opponent's lings. If you push your banelings too far ahead they will be exposed to stalkers or opponent's bio fire. From the terran's perspective you should be sniping those banelings and your top priority. Besides that you have to target-fire opponent stalkers or other marine-marauders and completely ignore the lings (and zealots obviously). If you are the aggressor be sure you dont overcommit. Your opponents can reinforce faster and a single injection can get your terran's army killled untill your lings arrive from your base. Always keep in mind that you dont necessarilly need to go for the kill, just show them you have what it takes and gain the economic advantage you need for a safer win. Proper micromanagement translates into lowering the ling count (having the opponent zerg larvae burnt) and the stalker's numbers decreased so that later on the Colossus ball will be weakened.
Firstly and depending on the map you are playing you should always know when your opponent zerg throws down his pool and he's gathering his gas. So you should be scouting early on regardless the map. On certain stages, those with a non-mutual choke point, you should go for a fast pool. Even if your opponent picks a 14pool you can always be aggressive (dont overcommit, remember his injection is coming out soon). Having a large marine or bio overall count is important early on to keep you alive. When you decide to push out you should have two things in mind. If the battle is hardly even you need to think about zerg's next injection. If you have the lead on zerglings you should go cause you have an additional 10 seconds on his next baneling cocoons. If you want to play with a fast reactor you need 3 marauders from your tech-racks to keep you alive. Stimpack will be delayed till your second reactor. If you somehow get past the early stage into Lair and factory/medivacs and depending on the pressure applied and your economy (if you get the lead at some points dont overdrone just throw in 2 to 3 at a time) there are 3 options for the zerg:
A. You go for a Spire if your economy is strong enough - start with 3 geysers, get the forth when the spire is midway and you need around 40-45 drones to start poping those mutas.
B. Go for the Infestation Pit if the battlefield is too open and your line of sight is extended (Overlords/Creep and Xel'Naga) because you can pretty much terminate any lings or banelings runby and you can cause major damage to bio units. Also, if your opponent is going Mutas you should be safe before he hits a critical mass. Infestor is overall a really good unit in 2v2 environment. Its low on larvae cost and its decent in multiple roles. Another plus is that they synergy best with terran mech and you can shoutdown low ranged units (like roaches).
C. Throw down a roach warrent and an evo chamber. This is a strong transition from the ling/banelings because those roaches are quite resistant against that and depending on your economy there are a lot of upgrades to get. You should get them in this order a. fast Glial Reconsitution (roach speed) b. Burrow c. Ground Carapace lvl1 d. Tunneling Claws. Also, depending on how long you want to invest on them. If your opponent go heavy on Mutas add a hydra den but dont go heavy on them. Their immobillity makes them not worth investing a lot. Overall this mirror matchup is too random so dont get discouraged if you loose.
Versus this combo you should feel safer throwing down a later pool because the protoss players usually favor warpgate pressure over gateway zealots. Nevertheless scout. In the early game you have the same rules and standars as in the previous matchups. Although pass the early stage there are some deadly combination they can throw at you, mostly based on their economy. The most popular scenario is zerg going mass mutaling and protoss building a two base powerfull colossus ball. Few things you should have in mind:
A. 6 colossi can kill ANYTHING in the ground before Ultralisks with their unmatched range and forcefields. Usually his zerg ally will keep pumping mutas untill he has the supreme air control. When he is sure that the Colossi can not be hit by air they will walk over your bases leaving only scraps behind. You should never loose the air control in this case. If you have to add corruptos/ravens/thors do it. Be sure you maintain the advantage but also note that with the latest tank nerf a transition to hydra/worm or hydra/masscreep can be leathal cause forcefields are too good against banelings.
B. The templar/infestor is a real killer. Few things you can do to stay alive. Fully tech ghosts to support your bio and the zerg should really just mass roaches with all their upgrades including missile attacks.
Mutalisks in the air and tanks in the ground is a very strong combo. The lack of a zerg opponent should let you setup a 15 hatch in a majority of the maps. There is still a possibility of being owned by 5racks/4gates but usually with decent tank placing and your lings absorbing some damage you should be ok. Be sure you dont get tanks on maps they can just skip the tank line into your base (War Zone/High Orbit). Containing your opponent is too good and too strong. If you manage to achieve it. Take Tempest for example. Opponents anticipating that will rush you or tech straight into Blink and try breaking the contain early on. Keep adding tanks, turrets, engineering bays in your contain to make it unbreakable. The most critical moment is when you are trying to set it up. The longer your opponents are contained the lesser their chances to break it later on are. If they go fast Phoenix the first six will be out harassing you before your spire is done. However dont get corruptors immediately. Remember they have low ground interaction. If you dont want to play it this way you can casually rush but be sure you deal major damage. If they plainly defend behind their wall they have an advantage. You team is mining on around 45 harvesters while they are mining on around 60. Apart from that every other option is valid.
This is a deadly combo early on. You need to constantly have the knowledge of what their tactic is. It is certain that at some point they will rush together the zerg. This is too strong on maps with seperate bases. The golden rule (after a lot of testing and looses) is:
A. 10pool counters 2x6pool
B. Overpool counters 2x8pool
C. 12pool counters 2x10pool
If you get rushed by lings x2 your lings should be out and your spine should be at 3/4. Use your drones but dont over-expose them. Create choking between your geysers with your pool and your spine. Micro your drones the best you can. After all you have 2-3 more drones than them and afterwards you are put in the darkness (will they keep massing?will they drone?). You shouldnt be expecting help from your ally. Single marine traveling to your base will most likely be picked up. If they 2x8pool/Spine Crawler rush you, you are in severe danger. Micro your drones the best you can and completely skip gas for the time being. You need to able to defend that and your ally should be arriving when the lings are dead. If you get 2x10pool'd with gas go for the fast banelings to defend. Scouting is very important. You never know when they are massing and when they are droning. You need to know before you fall vastly behind the economy. Pushing out early on before you establish a mass or superior technology is dangerous due to various injection timers. Also, watch out for muta feed (this is actually important for every other combo with a zerg). Once a zerg gets a spire its easy to have gas traded with the other guy commiting to lings/roaches. As the game proceeds be sure to destroy that creep they added.
Unless you can successfully rush them you need to play a long game. They way we play it; zerg gets a fairly strong economy. After defending their 2x4gates all-in (you should go roachling for that) build a strong roach/hydra army. Try to mass on that. They will most likely tech to Colossus/Void Rays. Dont get corruptos. Have the terran massing enough vikings (1 reactored starport for each base).
They will most likely mass bio. Nothing you cant shut down with mass lings
before Medivacs arrive. Play casual with your spire midgame, get infestors with
speed banelings too. If they both mech favor few fast broodlords. They work too good with Medivac support from your ally and they excel on breaking walls/the tank line later on. If they 4racks/factory bio/tank push you, you should have tanks of your own. Get the map control, spread creep and use your mutas/infestors to
Conclussion: Terran/Zerg is a powerful and dynamic combo. Its favored over the zergless combos whereas double zerg can be a tricky matchup. There is a whole bunch of possibilities to explore with your shared resources, some great timings you can hit for an attack and insane unit synergy to pick from. TZ rushes are really strong, dominant up to a point. Feel free to experiment outside this guide's frame. Afterall this is just AcidRain's and Honoratus' point of view and those are the commonest amogst the tactics we use. Focus mainly on the early stages of the game. Anything beneath 1700 points is going to fall to early pressure if it's executed correctly and mastering that phase of the game will lead you into a series of high quality games.
P.S. In the following days I will be adding some replays and perhaps screenshots from some of our games to compliment the wall of text :p Any feedback is always welcome and stay tuned for a major update the upcoming week!