doesnt matter, when you got the energy for it, use them, and keep sometimes energy for a scan in case a DT comes in or a Widow Mine drop. Well next tip is: try to get your natural expo quite early in the game, cause if you do it too late you will be behind a lot, and more income means quicker upgrades and units. Also pick a unit combo that works, like Marines, Mauraders and Medivacs. And always have a back up plan like mass air or Thor/Hellion