Terran Vs. Zerg
Defending
*NEVER make an outpost without giving it good defense. This is to prevent them from getting an Infested Command Center. If you think your expansion might be dieing lift off and get out. The last thing you want is Infested Marines coming into your base taking off 500 hit points.
*The main thing a Zerg player does is the standard 6-8 Zergling rush within the first 4-5 minutes. Then they might build massive amounts of Hydras. To prevent the Zergling rush you should build Barracks, Barracks, Depot, then continue to build whatever you wanted. If you are playing a small board like Blood Bath and the opponent knows you are close you will probably die or come close everytime if they know the 2 minute Zergling rush. I have used it and found it lethal almost everytime. I would just be ready to attack the Zerglings with your SCV's. Against massive Hydras use Marines with their upgrades. Bunkers will help but as you progress Seige Tanks will make them think twice the next time they go massive Hydras versus Terran.
*If you notice your opponent building a lot of Guardians then you MUST react! I would use Wraiths since Guardians attack ground only. Comsat a Zerg colony try to find the Greater Spire and if you do attack it by dropping Stim Packed Marines or whatever you choose. But since Guardians cost so much gas you should wipe out the expansions of the Zerg if they have any to slow the process of Guardians.
Attacking
*Firebats galore! Firebats are cheap, built quickly, and low in the tech tree. They Zerg are mostly land based so the Firebats attack almost all the units. A quick rush with Firebats and Stim Pack can wipe out a Zerg colony very easily unless the opponent has a high number of Sunken Colonies. And also since Firebats kill Zerglings with ease but they are less effective against Hydras.. But if your rush doesn't work, then I would say go with Seige Tanks. They are great if your opponent builds massive fleets of Hydras or Zerglings.
*Do not build a lot of Battlecruisers to attack with since the Zerg have Scourges. And a trade for a BC and some Scourges is not worth it at all.
*If your enemy is attacking in tight packs then use Irradiate to kill them. This can be very useful.
