Grand Theft Auto IV/Dimitri

Hostile Negotiation
The arrival cut scene puts you in a wharehouse full of Bad Guys ("BGs") crouched behind a short wall. When you get control back, sneak back out of the building and run around the left of it to the back where a building behind it has a staircase. Take it up to the top and cross over to the building and go left to the boarded over windows.

Moving around and aiming through the slats in the windows, you can snipe quite a few BGs while being very well protected yourself. Take your time to make sure you've gotten all you can. Shooting loose propane tanks will cause them to blow and kill BGs for you.

Once you have done all you can from the top level, go down to the next level and repeat, then the next level, etc. Finally, go back around and stop at the door where you started and start clearing out the remainders. The rest is fairly easy.