To do things 'before' exercise
1) Eat some light food 1 hr prior to exercise
2) Eat food is high in carbohydrate like potatoes/banana 1 hr before exercise to give energy (only do this if you are doing weight training)
"not to do things' before exercise
1) Do not eat and work out straight away
2) Do not have 'heavy' meals prior to work out
3) Do not take protein shakes before work out as this will make you feel tired (only drink protein shakes/bars post work out)