Stick a few around all your Missle Turrets and Tanks, Build more than you need so you can fully saturate your base and still be able to repair all your stuff. Plant a half-dozen SCVs behind every PF you create. This is extremely important for survival. Otherwise you'll end up behind and in trouble. You will be mining on that one base for the whole game, so you need to pace yourself and buy only what you need, when you need it. This goes for minerals/gas as well as biomass. So when budgeting remember to think about your day army as well as your night-time defenses. The more you kill, the more biomass you earn, the faster you are able to unlock your desired tech and the closer you are to completing the game. Kill as much as you can during the day. As such you will spend some Biomass on other units before getting Tanks, despite their importance. Note: good strategy on Hard is to let your Biomass stack up then buy Tanks ASAP when resource trading is enabled and you can pool your resources - on Brutal resource trading takes 20 minutes to become active, so this strategy does not work. Once you get them, Siege Tanks provide excellect ground defence when paired with Planetary Fortresses and repairing SCVs, Missile Turrets and Marines will take care of the rest.

The early game is the hardest part, as you are limited to bunkers and whatever units you can squeeze out to defend with.

This pretty much sums up the whole Hard/Brutal strategy in one sentence.

Left 2 die starcraft 2