Gears of War Act 1 - Fork in the Road
Marcus will have a choice here. Either he can go down the left or the right fork of this path. If you choose the left fork, you will be pinned down by a Troika gun emplacement.
So choose the right fork. Proceed down the corridor until you reach a turn at the end of it. Around the corner will be a Troika gun emplacement. Either throw a grenade or shoot the Locust manning the gun to take him out.
After the guy at the gun is dead, use the gun emplacement. Shoot the Locust that come from behind.
Use the button next to the door to open it. Enter the room and take cover behind whatever is nearest. There is another troika in the next room that is guarded by a couple other Locust.
Take out the Locust guarding the emplacement. Then take out the emplacement.
After the fight more Locust will come from behind. Use the emplacement and kill the reinforcements. When they're dead, a Locust come out of a door behind the emplacement.
Enter the door that the Locust just came out of. Follow the hallway and kick open the next door.