You fight AND do jobs.
Also pay close attention to tacticly timing using your daily energy pack. Sometimes it is better to wait than to waste it. Remember, you get to fill your energy when youlevel up as well. For example, it is not worthwhile to use an energypack if you are close to leveling up. Wait a couple hours and fight, level up , use that energy and then use your energy pack when it is worth the most. Otherwise you are throwing away free energy.
Also if you have a lot of energy and you are close to leveling up, get as close as possible by doing smaller jobs, and fight a boss. Thatjob is worth the most amount of experience. Your experience will carry over and go towards your next level up and you will have full energy. It may not seem like a big deal, but you can knock 2-300 points towards your next level up every time , you will level up much quicker over all. Use godfather points towards energy solely. The boxes are nothing special, and if youget 4 points for energy every few days, it adds up