When you are using Zerg race you must like with any other, adapt your game against the opponents. If your opponent chooses Terran there is one major tactic you need to know about. Those are Terran reapers. Highly effective when performing in large groups, they can swarm your base in no time. If you have trouble confronting such an attack this guide will teach you how to defend a Terran reaper rush.
One of the vital measures you will need to take is to upgrade zerglings speed. And I mean upgrade it right away, when you get 100 gas is your Q to start the speed upgrade at the sparning pool and than train some zerglings. Chase the reapers until you kill them all. You will have a large speed advantage, which is vital for victory. You could also build less effective roaches but they are often just slowing your overall progress as they do also very bad against marauders.
Another tactic is to get anti air very soon in the match. They will provide you with some defense against small groups of reapers, which are often used to tease you and to keep your scouts off their back, but do not fall for that. Also get some corruptors but keep your hand off mutalisks and marines. Important is to know what your opponent is doing so keep scouting his base to see what tactic is he using. Ground or air.
By using speed upgraded Zerglings and anti air defense, you will most likely defend reaper rushes successfully, while frustrating your opponents and getting them crushed.