Take a good pre (currently diggin the combo of the new jack3d dragon berry and yok3d) and rock out some whitechapel or black tongue while you lift. Right before a set, think about something that happened to you that made you mad. Could be an ex, a coworker, or something like that. Someone you want to prove wrong and show them what you're made of. That always does it for me. It's all in the mindset.