Stealth is always the best option. One of the easiest ways to do this is as follows. When you start, go up the stairs to your right. Before you get to the end, wall hug to check if anyone is there. If there is, take out your silenced PP7 and manually aim at his head. Then, shoot to kill. Crouch down and go along the balcony, silently picking off your enemies by shooting them in the head with your silenced PP7.