Scene 2 - Casino
You will encounter your first opponent just around the corner (screen). Kill him and order your men to take cover behind one of the larger objects. You should consider moving to your left, so you'll have a much better view at this corridor. Start using your sniper rifle and kill all visible terrorists from here.
Once you've secured the corridor, start moving forward. I would recommend using other objects for cover along the way in case you've missed someone. The next group will be waiting for you around the corner. Use the blind fire feature (screen) if any of the terrorists decides to get closer to your position.
Order your teammates to get here and move them somewhere to your left. Try killing all the terrorists from here. You should be getting closer to a much larger area filled with a lot of slot machines. Order your men to take cover behind the plant (screen). You should be standing behind one of the walls, preferably behind the left one.
Your top priority here will be to neutralize an enemy sniper. Look at my screen if you can't find him on your own. Once he's gone start shooting at the terrorists. Thankfully, none of the hostiles will even think about getting closer, so you can feel safe here.
As you've probably noticed by now, you won't be able to kill all the terrorists from here. Take a closer look at your tactical map. I would recommend moving towards the first room (screen). Once you're there, open a new door and take cover behind the right wall. This should allow you to target more enemy units.
You might want to consider allowing your men to move forward, especially since you'll be able to provide a covering fire from here. Prevent enemy units from getting too close to your teammates. It's also very important to take out a nearby gunner (screen). Make sure you've killed all the terrorists and start moving towards a new section of the casino.