During the start of the mission you'll only have access to a simple hatchet. You will need to sneak behind enemies and keep from being spotted by guards and search lights. When Reznov gives the signal, kill the unsuspecting guard and steal his gun.
Advance up the top of the building and press the button on screen to throw the guard down.
Enter inside the building and use your gun to kill a few guards below before they realize you are around. You'll be swarmed by enemies, but your gun and grenades are great for taking down every foe around you.
You'll be in Hudson's point of view for the next part of the mission. At first you'll be in a powerful vehicle, so use its heavy missiles to blast down the enemy. Next, you'll be exposed to the deadly Nova 6 Gas. Every time you are hit, your gas mask will start to break and cannot be repaired. If you breathe in the gas, you will instantly die.
The one safety is that your mask will repair if you completely die and respawn fro ma checkpoint. Hudson's gun has a great scope that will show enemies in night vision. This will be a great asset as it can be hard to see in the gas. Next, steal a rocket launcher and blast the two helicopters from the sky. You need to get a clean lock on and can't freely fire.
Upon clearing the gas, move to the small building below. This is a great sniping spot to kill anything that advances on you. Some will try to charge through the door on the left, but can be dealt with a fast melee attack.
Move into the last building and stay prone to get some easy shots in. Even in the clear, your scope is a great means for taking down enemies.
Retrace Mason's steps and clean up any soldiers and reinforcements that arrive on the scene. Keep following Weaver and you'll track down Mason. Press the buttons on screen to take down Mason once and for all.