When applying to grad school with a mediocre past how can you make yourself stand out
Why do you think you should be admitted?

The admissions committee will ask themselves: if this applicant has mediocre qualifications, why should we admit them?  Why should we believe they will be successful?  So, you should be asking yourself that question, and thinking about what your answer would be.

If you have a good answer to that question, that might tell you how to make yourself stand out: emphasize the parts that make you think you are well-qualified to succeed.  Your application is a chance to tell your story and answer that question for the admissions committee.