I recommend that anybody interested in learning how to get good at Alien Swarm and other tactical shooters refer to the US Army Field Manual for Combined Arms Operations In Urban Terrain. Specifically it jumps to Chapter 3, Section III: Clearing . I suggest reading most of this section because I believe it's very relevant to the tactics necessary to survive Alien Swarm.
NOTE: The Wikia editor seems to be failing miserably when it comes to adding external links. Search for "us army urban terrain field guide", should be a secondary link on the Global Security site. I shall try editing this later to add the link.
I first found out about this manual during my days as a Rainbow Six: Raven Shield player. It describes the four person fire team and how the US Army makes it work. There's a ton of information in the overall manual that's not really all that relevant to gaming but there are some really amusing bits scattered around. Really though it's the section on Clearing that provides a lot of insight on indoor combat for fire teams. It shows you how to handle rooms, hallways, corners, and intersections. It shows you how to enter a room given its shape and point of entry such that the team members can maximize their coverage of the area while staying out of each others sight lines. It also explains formations. It finally has a short list of verbal commands, some of which are helpful, others aren't very applicable, but it's a good place to start if you like the idea of adding it to your Standard Operating Procedure (SOP). Having a SOP, even if it's just a short and simple list, gives your team mates some basic things to keep in mind when the mission begins. Here's my initial one:
- Don't Panic
- Move As A Unit
- Mind All Sight Lines
- Have Fun