Figure out what you want to have done looking back from your deathbed, and work backwards from there. Literally just imagine you're old, at death's door, reflecting on your life. Really try to get into the role. Take some time with it, be thoughtful, don't just rush to an answer.

Whatever you think old-you would wish you'd've done at this age, do that. Spending more time in nature, exercising, reading more, connecting with other people, helping the less fortunate, whatever.