I took much of last year off to focus on learning the technologies needed to build the product for my startup -- graph databases was the big one, and during the time I built Bulbs (https://github.com/espeed/bulbs), a Python framework for graph databases like Neo4j Server.

Eliminating all distractions has been key -- no side jobs, no girlfriends, no going out -- a period of complete focus.

Working out and exercising has been critical though for keeping my energy level up and maintaining mental clarity.