The application process is not finished once you submit your application.
Prior to the application deadline you should follow up with the program to which you are applying to confirm that all application materials, including letters of recommendation, have been received. Give yourself enough time to connect with your recommenders, if necessary. You don’t want to find out after the deadline that you have materials outstanding, as in many cases this may negatively impact your candidacy.
Once your application is complete, send thank you notes to all those who submitted recommendations on your behalf and to anyone who helped you through the application process. Expressing your appreciation will benefit these relationships and increase the likelihood that mentors will be willing to write future recommendations for you.
Make sure to keep your recommenders apprised of the outcome of your application, positive or negative. If the outcome is not what you hoped, your recommenders may have insight as to how you can improve future applications.