Get someone else involved (Score 1)

What worked for me (and I'm assuming the original question refers to a personal project) is to start working with someone else wanting to achieve a similar goal.

Meet once a week. Analyze what you've accomplished over the last week. Outline what you're going to do over the next week.

Don't spend the meeting doing too much project design/planning--delegate that to be done over the week, then discuss it via email or during the meeting.

The accountability helps, but what really helps is having someone else who actually cares about the project enough to provide feedback, interest, and support.