Vs. Terran
A Terran vs. Terran game is a very interesting game as both sides have the same advantages and disadvantages. Basically, both teams have access to the well known tactics such as M&M and M3, (marines, marauders and medivacs, usually with the stimpack upgrade.) and the death push, (A huge all-in push of mechanical units, like thors and siege tanks.)
Early Game - Attacking/Expansion - M&M
Early in the game most Terran players will be building up their bio ball for their first attack. Scouting is, just like in every situation, a necessity. If your terran enemy is gasing up, they could be going for early siege tanks or an early starport for banshees. Generally this can be countered by a good sized bio ball before those higher tech units can get rolling. Also watching for a reaper rush would be helpful too. Attacking early on before your opponent has the chance to could cause your Terran turtle hide in his shell for a bit and could buy you time to get your first expo.
Mid Game - Mech/Air Warfare - Land Grab
Most Terran players will by now have a factory or a starport and will start getting out the higher tech units such as siege tanks and medivacs. Medivacs make the M3 bio ball shine but can meet problems when up against factory units. If your enemy is still going marines, consider getting hellions with the infernal preigniters. The bonus to light damage will eat up the marines. Also siege tanks can join the party to add splash damage to large bio balls.
Vs. Protoss
When the Terran goes up against Protoss, the Terran can really shine. While early on protoss units can prove a problem for barracks units eventually getting
Vs. Zerg
Team Tactics
Terran vs. Zerg can be a very tricky game. The Zerg early units are easy to make and can really do damage to a terran player early on. The Terran player has to be quick about his decisions and figure out what his opponent is doing before he is out massed with hard countering units. Each stage of the game is fraught with danger for Terran player, usually causing the Terran to turtle up while the Zerg player has the freedom to lay claim to all the minerals he wants.
Team Tactics
Zerg Nydus Scan -
When playing with a Zerg on your team you can assist in nydus worm placement. This requires the Zerg player to have a nydus worm and the Terran player to have the orbital command. The Terran player uses the scanner sweep ability in order for the Zerg player to make the nydus in the enemy player base. This can be used as a harrassing tactic to screw with the enemy, or it can be used to create a double pronged attack with the Terran attacking the front and the Zerg attacking the back, essentially making a super zerg-terran sandwich of justice.
Tips & Tricks
The Wall-Off
I know, I know what Terran player DOESN'T wall-off. Anyways I thought it was at least still important to mention so here we go. If you don't know what a wall-off is, it's basically when a Terran player, (yeah Protoss can do it too but this isn't the Protoss strategy page...), uses buildings in order to prevent enemy ground units from entering their base, or to buy the Terran player time as they defend against the attacker. The building mostly used is the supply depot, but barracks and bunkers also find their way into the wall-off. Wall-offs are usually just used on ramps that lead to the defenders' base, but are also found cordoning off expos or areas the defender doesn't want the enemy player from accessing.
Units -
Hellion - The hellion is a fast light unit that gets an attacking bonus to other light units. With the infernal preigniters upgrade from the factorys' tech lab the hellion gets doubled attack power 8-14 against everything and 14-28 against light. This is the first factory you can build.
