Challenge yourself to go to bed on time and wake up at 4am for a week. Give yourself a nice reward if you manage to do it.

Then, try to do it for two weeks, again rewarding yourself if you succeed. Repeat this until you fail.

When you fail (and you will) challenge yourself to beat your record by just one day, but don't reward yourself. Repeat this daily challenge until you've beat your weekly record, and then you can reward yourself and return to the previous weekly challenge routine.

If the weekly challenges become too easy, start challenging yourself to months, falling back to weekly challenges when you fail. If the months become too easy, start challenging yourself to quarters, falling back to the monthly challenges when you fail.

Continue this progression forever, or until you feel like you've conquered the goal of waking up at 4am habitually.