first of all, use energy packs when you just leveled up.
secondly, im pretty sure some of you never thought of demoting your mastermind before using the energy pack....
the mastermind gives you 11% more experience on jobs... it means if you demote him while using energy pack, you will be able to do more jobs
also important, to use the energy pack for the jobs with a bad ratio... and spend your normal energy on good ratio jobs.
when you are pretty close to level up -like 10-15 experience left- do a boss fight to take the rest experience with you in the next level.