Fill out your application completely. Attach an official copy of your transcript. Do not leave anything out and do not lie about any grades you have gotten.
Highlight the awards you achieved in college on your application form. Showing that you got numerous awards or prizes will help you present yourself as worthy of the master's course you would like to pursue.
Use the "additional information" section of the application, if there is one, to write a short essay explaining why your grades are low. Be truthful and honest about past mistakes. Use the section to explain what you would like to do with your life, how you have grown since your past school attempts and how you have changed your study habits and your life to ensure that you will get better grades in the future.
Find the name of the dean of the program you are applying to, and call or email him regarding your application. Introduce yourself, tell him that you have applied and mention that you are aware your grades are low. Ask the dean if there is anything you can do to show him and the acceptance committee that you are ready to work hard and that you are going to get better grades in the future. Request a private meeting if necessary.
Try again if you are denied the first time. Request from the dean or acceptance committee a short list of reasons that you were not accepted. Redo your application and try to improve upon it each time you apply, until you are accepted.