On the Tijuana mission where you get the sniper rifle and the man says, "Now the Federales 
are after me!", you are confronted by a group of men with rifles. They will be on the rooftop 
directly across the courtyard from where you are standing. The following is an easy way to 
dispatch them. Step to back into the corner and look just above the shack with the red roof. 
You can just barely see the head of each sniper, but they cannot see you. Take them out one by 
one until there are none remaining. You will save a lot of ammo by doing this. Then, go through 
the courtyard and around the corner. You are now rushed by several enemies. Duck behind the rear 
of the police car and snipe the men in the head as they come around the corner. You will save 
even more ammunition by doing this. Around the next corner there are several more lambs to the 
slaughter. Duck behind cover before you go any further. Make some noise so that they will come 
around the corner exposing themselves. Snipe their heads. Note: One of them has a rocket 
launcher; take him out first if you get rushed.