"Starcraft" can be a tricky game to dominate, with millions of veterans whose skills will easily put your knowledge to the test and destroy you quickly. The game's campaign mode begins with the humans, also known as Terrans, whose mission is to prepare habitable planets for population and fend off hostile alien life to ensure safe living conditions for future inhabitants.
Of course, the Zerg and the Protoss won't give in without a good fight, and neither will most seasoned players.
Included below are some tactics you can use to ensure the destruction of these hostile races bent on kicking the humans off their planet.
Start off quickly, as always
Of all the races in "StarCraft," Terrans are probably the weakest military-wise. You'll want to use your military capabilities as early as possible, meaning getting your SCVs (worker units) grabbing the minerals quickly. About ten should work to give you a steady flow of income early on. Get the Barracks built as soon as possible afterward, and start pushing out Marines steadily, using Supply Depots as a wall to slow potential early attacks.
As soon as you have one Marine ready, send him to where the enemy base is and see what happens. If this proves successful, set a waypoint from the Barracks right behind Enemy Lines and keep pushing out Marines. The advantage of Marines is that they are the only starting military unit with a ranged attack, meaning every other race will take damage getting close enough to strike.
If you can get them in before the opponents' military units are ready, you might find them mowing down worker units for an early victory.
If the opponent is more seasoned, get ready for more advanced tactics
If your early Marines aren't enough to make progress, just try to keep harassing them as you build more structures and prepare more advanced attacks.
On the defensive side, maintain a wall of Supply Depots with Bunkers behind them. The enemy, if ground-based, will be forced to take fire before they can even reach your Marines if you do that.
Build Turrets to fend off early air assaults as well, and do not ignore your production area. Veteran players will sometimes sneak in by air and kill off your SCVs while you work to defend your front lines. Without minerals and gas, your advanced tactics are as worthless as a wooden penny.
Guerilla tactics against the opposition
Try to use your advantage of being able to build anywhere and possibly build a Barracks behind enemy lines if they aren't paying attention. Their offense will collapse if their base is being destroyed from the inside and Marines are killing off their worker units.
Good luck on the battlefield.