you need to be very disciplined about quitting responsibilities, saying no, clearing your plate. A startup is more than a full-time job, do everything in your power to narrow your focus and avoid burdening yourself with commitments. in the same vein, be proactive not reactive. set aside a portion of your day for "work" and don't respond to emails or calls during that time. do what you decided to do, not whatever feels right in the moment. the feeling of progress will give you fuel to keep going.