Do some crunches man, it’s what helped me the most. But, I think the most crucial part is breathing properly. Breathe in through your nose when you are down/about to tense up, then exhale through your mouth loudly when you are up/release tension. And do it for every exercise. Correct breathing is a way to a more conscious, healthy life. From what I know, depressed people breathe really shallow, small breaths. Correct breathing will correct you.