I have been trying to work on all 3 characters, building them up. For some reason Trevor is far ahead of the other two. Every stat seems to raise quickly for him compared to the other two. Especially his Strength, which I can hardly get to budge on the other two. Any tips?
So far I have found that:
Stamina is very easy to raise, just run a few marathons.
Flying seems easy too, just do the flying school and it was maxed for Michael
Shooting, shoot lots of people/shooting range
Stealth, Hunting seemed to help alot for Trevor. Just sneaking around away from cops or in missions, etc. It raised very quickly in hunting though.
Strength is just slow as molasses though.