Easiest way to level up fast is to go out free running at night! Your agility and power points will double during the night so this is a great time to go out and earn some points. Why not deliberately go and pick a fight with a volatile? Let him chase you, keep running like the wind and let more and more come after you and your agility points will soon start racking up, especially at lower levels and you'll have this one in no time!
Just don't run to a safe house, this will cause your pursuit to come to and end and your points will stop. If you survive the night and you want to go again just sleep at a nearby safe house and prepare for round two.