Create a to-do list of projects that don't have a deadline.
See that blank space in your schedule? You can use that time to play video games, go shopping with friends, or learn to skin an entire moose using only a paring knife. Just kidding! Your second tool is a to-do list, where you write down projects that don't have a deadline. When you have unscheduled time, you do the tasks on your to-do list and check them off when they're done.
Your to-do list grows forever, like the interest on your credit cards. You'll soon have a million items on your to-do list. How to choose which to do next? I recommend the Superfocus System by Mark Forster.
Where to keep your to-do list is a surprisingly hard choice. I've tried dozens of to-do apps and always returned to paper and pen. Check out my episode on choosing the perfect tool for more details.