Once upon a time, terran vs terran was a stale matchup, where players would just cower behind tanks, turrets and battle cruisers but in the StarCraft Two era this is no longer the case. Today TvT is one of the most dynamic and exciting matchups that exists.
Generally the best play in terran vs terran is to go for an early fast expansion after you build your depot, refinery and barracks. You are almost always going to want to plant this on location to get your economy up that much faster. In this matchup you don’t need to send your reaper to go scout and attack right away because usually your opponent is going to have a reaper too so just positioning your reaper defensively can be a good idea.
There are a lot of different strong openings in TvT. You can get right on that marine production with a 2-1-1 build and use your stimmed marines to hit in multiple locations at the same time. You can also tech up to banshees right away, potentially even with a proxy starport but even just at home, and then try to do some damage if you catch your opponent without scans or missile turrets. Another option is to try for a quick widow mine and marine drop and aim to do some economic damage right away.
Cyclones are useful early on in fending off any aggression or harass but lose their utility as the game progresses so you seldom want to make one or two. These units are also powerful attacking units during the early game so if you want to get aggressive this is one way you can do so. Generally the safer bet is to go for an economic build and defend but it can be fun to go on the offensive early on sometimes too.
You don’t have to use bio in TvT although it is by far the predominate choice among progamers. Gumiho has demonstrated the efficacy of mech quite impressively in this matchup. Generally he would use a turtle mech style, setting up defensively with missile turrets and then building up to a strong mech army of tanks and thors with hellion/hellbat support and then moving out. The problem with this strategy is that you lack mobility and bio is highly mobile so it will be difficult to defend against drops and harass but the mech army does pack an impressive punch.
TvT is a very tactical matchup and having the right positioning when you engage is very important. You can also split up your army in order to menace in one location, drawing your opponent’s forces away, and then strike in another. Because of the easy availability of mass medivacs doom drops are always a tactical possibility and having sensor towers and missile turrets in place is an absolute necessity.
Air control can become extremely important during engagements. Having a squad of vikings will allow you to have vision for your tanks and your opponent will basically be forced to burn a lot of scans or lose ground as you covertly unsiege and advance. Liberators can also be worth their weight in gold when you both have a tank mass because they can siege up on the edge of the tanks and force them to retreat.
Not losing your army by running it into tank blasts is an important skill. You must always be vigilant to control your army well because two quick volleys can wipe out a game’s worth of production. Upgrades are important in this match up as in any other. In particular marines that have stim and combat shield just wreck those who don’t, so if you do fall behind on these upgrades don’t engage until you have caught up. If your opponent is ahead in attack and armor upgrades then you definitely do not want to have any marine on marine skirmishes and you will have to retreat to the safety of your tank line. Maintaining a strong map presence will prevent your opponent from gaining ground and laying siege to your bases.
TvT is often a matchup where action occurs simultaneously in many different parts of the map, so it will test your ability to multitask and simultaneously defend and attack. It is important to stay aggressive and always be trying to get the maximum utility out of your units and keep your opponent on the defensive. If your opponent leaves his minerals lines defenseless then get in there with drops; stimmed marines can take out a ton of workers if your opponent is slow to react. You can also use liberator harass to target exposed enemy scv lines and then fly away to hit another base or just lurk and return to the same one later. The important thing is to make sure that none of your units go to waste and always be trying to get additional utility out of your faces.
As TvT progresses to the late game you are going to want to get a strong and more cost efficient army. Ranged liberators and tank masses become very important, and you will want to be producing out of more than one starport and factory. It is crucial to max out on all of your upgrades, not only 3/3 for your infantry but also getting the vehicle and ship armor and eventually attack upgrades as well. You can build a few spare orbitals in order to be able to call down a lot of mules all at once and you will want to have all of your most exposed expansions as planetary fortresses in order to prevent any light harass from doing serious damage. A few ravens can also be used to cast spells during bigger battles.