StarCraft: Brood War/Terran Mission 1: First Strike

Meeting Duran
You start with a well-established base with plenty of minerals, but not a whiff of Vespene. You need to find a geyser, so just build a couple Marines, then send your Marines and starting Siege Tanks east. There's an enemy Barracks and some ground troops here. Take it out if you want, but the enemy will keep delivering units via dropship, so don't stick around. Head north to Duran's base.

Destroy the Command Center
Duran's base has a Geyser, which you'll need, and he also informs you about a "back door" to the Dominion base. Set up a few siege tanks and bunkers for defense, but you won't need much else. Crank out siege tanks and marines for support. When you have one group of each, march up the north passage. Just siege your tanks whenever danger threatens, and you'll clear out most of the opposition. The only tricky bit is the buildings on the ridge to the north. You can't target them without a ComSat sweep or by sending units up the ramp to spot them. Still, it's only a few infantry on the ridge. Once you reach the command center, siege your tanks and pound it until it's destroyed.