Map
The world of "Scarface" is broken down into four principal turfs: Little Havana, South Beach, Downtown and North Beach. Start with one turf and criss-cross every street on the map in that area until your map shows a red skull icon denoting a gang leader. Take out this gang leader first, but don't let his minions scatter afterward. If they survive and get away, you won't take total control of the turf, and the skull icon marking their place will be absent in the future. You can also open your stats menu to find out how many gangs are left in each turf.
Police
Another potential spoiler for your gang conquest can be the police. If you cause too much commotion and destruction in your gang battle, the police will show up, making your job more difficult both by firing on you and allowing gang members to get away. One way to avoid this is to let the police fight it out with the gangs and the gangs alone. If you hear sirens, holster your weapon and when the police show up, they won't fire on you -- they just shoot at the gangs. Let them have it out and take out any leftovers.
High and Low
Finding gangs can occasionally be more difficult if they are hiding above or below street level. Around the edges of the map, look for bridges gang members have congregated beneath. This can mean one floor down near the base of the structure, or even lower near the water. However, gangs can also be found above you -- in the downtown highway overpasses, the gang is located at the very top of the ramp.
Weapons and Strategy
Take careful consideration into both the weapons and vehicle you bring into a gang fight. You must be ready to battle several enemies at once, so choose a car with high defensive properties such as the Bodog. This vehicle is also capable of taking out several enemies at once, lessening the chances of anyone getting away. You should also save your game as much as possible. If you die in the middle of a turf war, you will still get recognition for the enemies you've killed.