A habit I learned from Reddit is to keep a gratitude journal. One of my daily tasks is to update it with one thing from that day that I'm grateful for. It can be a big thing; it can be a very small thing like having a tasty muffin that morning. I update it even if my day was miserable and I struggle to think of something.
I've become a lot more mindful of things I'm grateful for (so I can update the journal). When I'm grateful, I worry less about sad things like death.