[Lostangel]

It is difficult, if not impossible, to get to the top without donating. I have donated $20, for some cash to buy items and for a decent house. The key to the game is to get the best house as soon as possible. The house allows you to train more efficiently (larger gains per point of training).
The only way to pass a donator is to play more often than them, since they can train almost 50% more often than you can (or train AND attack).
That being said, the best way to gain is to create a gang, or be in a gang with payouts.
Our family of gangs is good, because the elders really help those below them with improving their houses/equipment.