By bringing your focus back and being aware of your breath and paying attention to the breath going in and out. Just focus on breathing and just think of something that is calming and peaceful to you and that will help you with bringing your focus back .
For me, what I find is that meditation helps me find the positives in myself. I become a more positive person all together and it really helps build self esteem as well. Self discipline is one of those things you really have to commit to and work on A LOT. What I found was that making it something that is simple, yet will make you really try to keep working to get it back would be a good way to discipline yourself.