this is how to beat every level:

Aace Bradley: In this stage there is a target at west,east,northwest and northeast, shoot the northeast guy first then the east, northwest and then the west guy

Tony Carter: First of all buy a scope and shoot at the thing holding the eletric wire

Mike Fernando: Just shoot the guys from left to right and leave the guy with a sombrero for last

Ernst Zimmerman: Just wit until a guy with a hat appears and shoot him

Anders Magnusson: This is the hardest of all,shoot at the window in the second row counting thirdteen windows from left to right

Johan Kristoffersson: Kill the guys from right to left because the last guy will appear from the left side and he is very fast

Stanislav Petrov: Just shoot the two guys fast because if you shoot one of them the other will shoot at you

Athir Nasri: This is the easiest one, just stand still doing absolutely nothing and you will win

I suggest using the Steyr AUG with all the mods on the night missions and doing the easiest missions first to earn money