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Create a Jira issue explaining your change. If it is a bug fix or an improvement, you can use the Community Reported Issues project.
Create a local branch with the name of the Jira issue and check it out. This way, your changes can be easily identified. Create the branch in the remote repo also.
Make your changes. Try them until you are sure they work as you want, and everything else still works.
Write or update unit and integration test procedures. There is a great guide about how testing in Open edX works here. You can also learn from the Django testing documentation.
Run again the tests for your applications. Pay special attention to your new code.
Commit your changes to your newly created branch. Be as clear as possible in the commit message
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