Chapter 1: PrologueEdit
The first chapter serves as a sort of tutorial, but it isn't a total walk in the park.
After you gain control of Hayden, continue on down the stairs. Leap over the wall and jump through the window. Smash open the box of ammo on the right and shoot the lock off the door. In the room with the slideshow about Enferon, plant a C4 charge on the second pillar on the right and continue through the doors ahead.
Once in the shower room, go towards the corner to the right and forward. Kill the soldier, take his AKS-74, and plant another C4 charge on the wall to the right. Keep continuing and kill the various soldiers in the next rooms and hallways. Use cover and aim for headshots to take down the enemies faster. It's not necessary to take all the ammo the enemies drop, but make sure you always have enough to take down any foes you come across.
Once you get to the locked door, shoot off the lock and watch the cutscene. Afterwards, continue through to the warehouse. After killing all the soldiers, walk up the stairs and sprint across the catwalk to avoid the helicopter fire. Plant C4 on the wall on the left and grab the ammo box, and run to the alcove on the left that has a metal Weapon Crate and a Rocket Launcher, and pick up the Rocket Launcher.
Ignore the helicopter for now and kill all the soldiers who are coming after you. The Rocket Launcher makes this very easy; just make sure to keep a good supply of rockets using the Weapon Crate in the corner.
After killing all the soldiers, the helicopter will emerge again. Lock on to the helicopter by aiming at it until the reticle has completely zoomed in and a beeping sound is emitting. Fire at it until you hit it three times, or six times on Brutal difficulty, to take it down and finish Chapter 1.