Previous experience as p.e. teacher is a major factor or previous experience teaching anything else also helps.
Other actual skills that could make you more desirable is how well you work with others, most p.e. teachers work in pairs or groups depending on the grade. Classroom management skills because highschool p.e. class tends to be the largest and most active class. Further more, skills in a particular sport so you can coach said sport as well as teach p.e. Football is a big plus as well as basketball depending on where you are at. Soccer is also starting to take off as well. Other sports that wouldn't hurt to have experience in but not ideal would be volleyball, tennis, cheerleading, lacrosse, track and field, cross country running, golf, and wrestling.
Most importantly skill to have though if you want to secure a position as p.e. teacher or health teacher is to be known by the principal and faculty. A principal is more likely to hire someone they know vs. someone who is very skilled.