"Pursue, keep up with, circle round and round your life, as a dog does his master’s chaise. Do what you love. Know your own bone; gnaw at it, bury it, unearth it, and gnaw it still." --Thoreau (in letter to Harrison Blake, March 27, 1848)
You can't wear out that bone. It will serve you, delight you, nourish you. Don't ever stop playing with it.
What do you love to do? What labor of love would you start today, if you knew you could not fail?
If there's a book you dream of writing, start one page. Don't worry about Page One; take a stab at Page 87.