Hi,
You want a great overall resume, or be one of few students in your class to apply to your own program.
There aren't any real "secrets" to what makes a great resume:
Extracurricular activities- SGA, endo club, endo lit review, or anything else that interests you.
Research- ideally in an endo field. Publications cannot hurt!
Endo involvement- AAE meeting, read the journal, endo CE
Letters of Rec- if you can do research with a known Endodontist in your school it can only help
Go to Penn, Columbia, Harvard or Uconn- those students were disproportionally represented in my interviews.
Write a good personal statement.
Once you get the interview it seems personality is most important factor. The selection process does seem random once interviews are given out, you never know the X factor that will tilt the scale in your favor.
Stay safe!