Most of people miss deadlines because of procrastinating too much. In high-school I was a hardcore procrastinator, I was missing every deadline because of my procrastination, It had gotten to the point where I did not have anymore excuses to tell to the teachers in order to buy me some more time. Then I started realizing that something had to be done, and I started thinking about thing that I could do in order for me to never miss a deadline again.
Here are three simple things that would help me don't miss my deadlines:
1. I wrote down everything I had to get done. Just the fact of having them written down helped me me take seriously everything the things I had to do.
2. I would tell everyone I know that I had already started doing it or sometimes that I already finished it. I find pressure to be a great motivator, and if you choose to tell these "lies" to people that you don't want to disappoint the pressure will be even greater that way you will be sure to not miss that deadline.
3. If you know you got time before getting your job done, then start doing it little by little. Don't procrastinate into thinking that "you got time". Trust me, having your work half done will motivate you to finish it and a slowly planned and well thought work is much better than one done in a hurry.
As you can see not meeting deadlines has a lot to do with procrastination, and as an ex student I can say that the habit of procrastination is the worst habit one can take. I hope this tips helped you and always remember that self discipline is the key to everything.
-Roger