OK the first parts are easy until you get to the counter sniper. You go to the right side and prone in between two windows. You wait till he fires, you get up and look to see where he goes. If you miss him just do the same thing again. Prone right after you fire and it takes 3 hits to kill him. I pick one window (If there is two he can pop out of) and focus on that window.
If he is not on that one I just prone. On the next part after that you want to snipe the people in the windows, I usually leave the one right after you un prone in the right window alive to not waste my time. Go up the stairs and jump out of the building. After you shoot the flamethrower guy pickup the PTRS (only if you want to) and wait for the guys to come at you. One or two will come so kill them and take the MP40. Advance as best as you can (I cant remember this part that much) and then when your sniping their troops just hit the other people in sniper locations and those on turrets. If you get hit dont risk dying. Wait for your team to clear the building and advance to the next part. The next part is pretty easy, amd you should soon be at the end.
You HAVE to kill his counter sniper because they one hit you. Kill some of his body guards and you will be off to the last bit. You want to run from the grenades and then let your guy deal with the people who run up the stairs. Then your done! Tell me what one you want help with next.