What do we do when we've broken a precept?
Don't regret or repent! That is bad Karma. What you need to practice is Samma Vayama(The right effort) of the noble eightfold path.

The effort

(1) to prevent the arising of unarisen unwholesome states;

(2) to abandon unwholesome states that have already arisen;

(3) to arouse wholesome states that have not yet arisen;

(4) to maintain and perfect wholesome states already arisen.

Take the triple refuge and the five precepts every morning to remind yourself. Then at night, before going to sleep, reflect on the day's activities and see if you broke any precepts or if you can improve with Samma Vayama and try to do better next day.