what makes you happy? go, find something you enjoy doing. go through the process and see how it turns out. hold onto the frequency of joy and love. hope this helps.
Aside from that, be decisive, active and productive. Push yourself into things, get some new hobbies and get out there.
Take up a sport, or just get into fitness. Exercise increases oxygen flow and releases endorphins. Climb a mountain.
Being indecisive is something that can strangely drag the mind down, I find. Don't dwell on things.
It's hard to get up and get anything done when you're being dragged down, but if you can push through and do it anyway, you will almost certainly feel much better for it.