I’m a Gold League 2 Terran player, and I’ve recently discovered an early-game strat which I think GL2 & below Terran players almost always overlook, which is very helpful defending against early-game Terran & Protoss harass (not Z).
The simple strat is: build a raven as your first starport unit (unless your going for super early aggression yourself), and then hotkey it to (say) 3, so you can call it over immediately as soon as needed, and/or pull it away from front lines if you F2 your army.
Ravens are seriously underestimated by lower-level players as a defensive resource. Here is how it works:
*Ravens have detection. They are therefore very effective against early-game DT warp ins, if they do happen to get into your base. Missile turrets are not as effective as they can’t shoot up and the first thing DTs in your base will do is kill the missile turrets.
*Ravens can help defend against oracle harass. You can drop an autoturret in your mineral line to ward them off, or use interference matrix, giving you time to get your units into position.
*Ravens can be used to clear out any observers lurking in your base to deny your opponent knowledge of what you’re doing.
*Raven’s detection helps defend against early game clocked banshee attacks, eliminating your need to build missile turrets early and/or expend CC energy on scans, which sometimes won’t be available.
*Ravens can help defend against liberator harass. You can use interference matrix, allowing time to bring units across, and/or drop and autoturret.
*Ravens are very good at dealing with enemy siege tanks as part of an early game drop/harass. Fly over, interference matrix the tank and then fly away. You can then push your marines/tanks forward and take out the tank.
*Ravens can also interference matrix an early game battlecruiser warp in. By disabling it, you can use your marines to take it out.
More generally speaking, a Raven also spares you the need to build missile turrets too early. Many lower-level players build missile turrets to defend against early harass, but do so too early. Missile turrets are expensive early game - it takes 100 minerals to build an engineering bay, and another 100 minerals for each turret on your main & natural mineral lines. When you add up the time SCVs take away from mining to build these, that’s nearly 400 minerals - enough for a fast 3rd CC or 8 additional marines.
Furthermore, two turrets is not enough. One turret will not defend your mineral line against a liberator, which can be angled in out of turret range and still hit your SCVs. Same with banshees to a lesser degree. And it won’t prevent drops, which can be done outside of turret range. Turrets are too expensive and not effective enough early game. You need to wait until your economy is ramped up.
Ravens are an excellent substitute (coupled perhaps with a cyclone as well) to the role often played by turrets, and are much less expensive.
Try it out. I think it will help a lot.
Warning - make sure you hot key it so you can separate it from your entire army if you F2 in an emergency. It’s very important not to fly your raven headfirst into an oncoming army an lose it.