[oxplot]

Deadlines: perfectionism isn't an issue in itself, spending eternity achieving it, is. Pick a milestone (e.g. MVP of feature X) and a due date. Once you hit that milestone promptly, pick another and repeat.

On a different note, perfectionism can be a symptom of procrastination. It requires much less will power to fine tune an existing thing, than it is to start something new or work through early steps. If this is the case, then apply the usual anti-procrastination techniques: vow to put X minutes a day into a project in order to make it a habit and get the ball rolling; identify obstacles that are creating friction; re-think the design and simplify; breakdown the task to make it less intimidating; etc.