If you don't have much HP then just make it count when you can. Adding to existing votes or discovering content that others will vote on are key. Just try not to waste it.
I would advise to power up all you have unless you need to cash out.
I can remember well when my vote was not worth a cent. I tried to add value with my comments.
Right now I'm powering up. Gathering as much HP as I can. I don't need cash for now. I'm working to add value to other people's post and also create original and meaningful contents.