I don't want to brag, but... http://steamcommunity.com/sharedfile.../?id=104013892
Terror missions would usually go two different ways: either the X-rays would zergrush me, so that I only ever see the starting area of the map, or I needed to run & gun to prevent a zombie outbreak.
When Cryssalids attack I noticed it's more effective to have something resembling line infantry like in Napoleonic times rather than staying in cover. Of course, that doesn't work if anything else is around with grenades, like a Sectopod, Mutons, Floaters or a Cyberdisk. So keep them together while spreading them out. Sounds easy, right?