I think the key to short term, day-to-day energy, is radically changing your state (as my boy Tony Robbins would say). When feeling tired (lets say while doing something boring such as paperwork, or answering emails), you can literally stand up, jump around, do some push-ups, or anything to get your heart pumping. Sometimes this will be as simple as standing in front of the mirror and putting some headphones in and act like you are getting ready for a fight (which works wonders by the way).
But lasting energy, and motivation (the type Grant Cardone has) is deeper. It comes with KNOWING and COMMITTING, as Alida McDaniel commented that today has to be a day that you use to further your mission. Knowing that each day is a chance to create positive momentum in each area of your life and YOU are the one in control of it! Another Tony Robbins insight; PROGRESS IS THE KEY TO HAPPINESS.
Grant Cardone, thanks for all you do man!