There are missions that require energy in order to complete. Dates will also require energy. Tackle them one at a time. They will become increasingly difficult as you progress, and will require more energy to complete. Concentrate on completing one before starting a new activity that requires energy. Also try to start such activities when your energy bar is full. During on an energy mission, you can perform different actions that cost varying amounts of energy. You will usually get as many stars or hearts as the amount of energy spent. Sometimes you might get one more star or heart, especially after higher energy actions. Look at the stars or hearts below the action and decide how many you need to collect in order to ace the mission. Never start an action if you cannot complete it.