Advance up and around the corner. Stick close to him and use the metal beams for cover. Crouch behind the set of bars in the center, right where Soap usually takes cover. Grab the RPG and turn to the left. The helicopter is coming around for an attack run. Line up a nice shot and blow it out of the sky right before it opens fire.
With the helicopter gone, just focus on mopping up the Russians. Make sure that no one is waiting to the right. They can flank you easily from the side room. Then blow up the gas tanks ahead of you to thin out the Russians. Follow Soap through the side room and kill the few Russians in here. Then advance a bit further.
You need to listen to Soap and split up. Clear a path through the soldiers and then climb the stairs. Swing around and ambush the group of 5 soldiers rushing down the platform toward the main group. Then link back up and charge up the stairs.

click to enlarge
There's a big battle coming up though. The Russians will pop smoke and use their thermal vision scopes to take you out. You'll have to do the same to them. Stick to the right side. It has more cover and Ghost usually sticks around to watch your back. Keep an eye on your surroundings for Russians moving up on the sides. The focus is at the end of the platform though. Use a thermal scope to wear away at the gunman on the balcony behind the smoke. There should be about 7 or 8 in the windows. Once you take them out, it's easy to mop up the men on the ground.
You'll get a special note that the hostages are possibly wired with explosives, once the area is clear and ready for breaching. Go up and breach the closest door. The entire room is filled with explosives, so watch your fire. There are 4 soldiers. One is right in front of you and will do a melee charge. Nail him and the soldier right next to him. Then hit the 2 in back. If the furthest one back is too difficult to hit, remember that you can still aim down the sight. It will just seem really slow. Once the men are dead, you're done.
Follow Soap out and jump onto the helicopter to finish up the level.