Top of the class and great boards are a good start. Without them, all the extra curricular activities in the world do little to compensate. With that said:
some good externships for OMFS
Some involvement in school, student government, research, etc.
Letter of rec from OMFS chair helps, as well as personal deans letter
involvement in ortho program at school
Attend orthognathic conferences, CPC's, other conferences at school on your time
Some type of ortho mentorship which involves workups and basic tx planning
Dress well for ortho
Just some things I have seen on applications. I am sure there is more.