When playing as a Maniac, you can earn one new energy point every three minutes (as compared to five minutes for other types of characters). More energy allows you to do more jobs.
Fighting
For lower level players, fights are importing. Because they only offer between 1 to 6 experience points per stamina point, fights will not really help you to level up. However for players with a lot of stamina points, lots of health (or money to heal), fights can help make a difference. Note: If you fight too often or keep hitting the "Fight Again" button, you will make enemies. If they snuff you, you can lose just as many experience points.
Saving energy
When building your Top Mafia, put a Fearless character in the Wheelman position (the higher the level, the better). By doing this, you will use up to 11% less energy when doing jobs. This will also increase your chances of completing jobs without using any energy.