Sun Tzu said:
To win a glorious victory
1) Hand over huge amounts of money to a company called Gree
2) Tap away on your phone/tablet for three days solid
3) Avoid SAS, just beat up weak teams
And there you go, no strategy needed (apart from avoiding SAS) and you can walk away with your war booty. Which is a few pixelated weapons and the admiration of everyone in Crime City for wasting your time and money on a pointless game.
Taddah!