Make it a point to actively engage in something interesting but unfamiliar to you throughout your life. Something fun and challenging to learn. Something that requires dedicated attention and has the potential to bring unique fulfillment to your life.
Start with your interests so you can tap into your creative energy and keep it activated. Make it something unfamiliar so you can constantly have something to work on beyond the edge of your current ability. Not only does this promote an essential humility, but it also keeps your mind sharpened against the dulling effects of comfort and predictability.