To clear out a room, stand besides the door, as one of your teammates would have if you told him to clear out a room. Make sure that your clip is full and the action icon does not have the brackets around it, so your teammates will not open it for you and take fire. Finally, make sure that all of your teammates are stacked up properly:
(for double doors) _____ (for single doors) ___ * * * * * * * *
Then, rush the room with thermal/night vision (your choice) on and scan left to right for enemies. Then, strafe to the left of the door to let your teammates in. Next, walk around the perimeter of the room and when your teammates say threat neutralized (on some smaller rooms they do not say anything), your work is done.
Garage: Capturing Emilio Vargas
In order to capture Vargas you need to move fast. This will cause you to take some damage, but to take out enemies quickly use the HE grenade launcher or the Red Phosphorus grenade launcher. Use it on groups of enemies as you are chasing after him. This works best on the two guards in the cafeteria style room; if you have not caught him yet, you can shoot the grenade off the wall and take both out without stopping.
On the first level that you are in an oil refinery, take an HE grenade launcher as your secondary weapon. At the end when the enemies fire RPGs, take it out. Step out from under the roof area so that enemy fires an RPG. Three enemies will appear. Shoot an HE round to kill them. Move back under the roof, reload you HE Grenade launcher, and wait until a second RPG is fired. Move around the corner and with your HE grenade launcher and shoot the man that is standing there. Turn around, and when the garage door opens, shoot the barrels on the right side with your primary weapon. Kill all enemies, secure the hostage, and the level will be completed. Note: It recommended that you save the game when you open the door that leads to the RPG area.
After every fire fight, reload even if you have 22 rounds remaining. If you keep doing this, you should have enough ammunition for the long fire fights and levels.
Glitch: Full clip
Press "Reload" ( [X] by default) before you use a full clip, you will not lose that clip. You will get a free full clip.