I did some experiments with diet, tl;dr is to eat a mixture of sugar and fats a few hours beforehand, then coconut oil afterwards helped, the full thins is in the thread below:
I’ve stuck with that system and it continues to work for me, I’m in no way being a jerk when I say your psychic/magickal muscles will build with time, so each time the big work that tired you out will become easier, and you’ll be looking for bigger goals. 
Also, learn a well-respected energy healing technique (there are loads, and information all over the internet) because sometimes you will need to “refuel” with more than ordinary nutrition.