From what I have seen with family and friends kids playing football and being a HS football fan....
1. Crete connection with feeder programs and elementary schools in your district. Team reading days, welcome the kids to school, team building activities, etc.
2. Have camps for all levels in the summer, spring, and/or winter. Teach the fundamentals but allow the kids to play games and have fun.
3. Create a children friendly game day atmosphere or have special days to get families to bring their kids to the games and watch the on-the-field product. Trunk or Treat, PeeWee Night, etc. Get the kids and parents interested in your program. Many schools let kids form a tunnel on the field as well.
4. All kids should get a decent amount of playing time in Freshman. No kid should sit the bench the entire game. I've seen many kids who were not good as freshman turn into All-State by Junior/Senior year. You don't want to run anybody off because of playing time.
5. Let kids join late, especially at the Fr/So level.
6. Build confidence in the weight room. Coaches know weights are important for speed, strength, injury prevention, etc. but kids don't see it this way. They just see their numbers. No matter what the gain, celebrate it.
7. Coach kids how kids should be coached. You can't coach every kid the same way, you have to learn their personality. Some kids can take a good yelling others can't. Have your coaches learn the personalities of their group, allow them to coach the kids the way the kids need to be coached.
8. Know when to lighten up, not everything has to be 100% focused all the time. Make practice somewhat fun for the kids so that they don't dread going day after day. If you being big game and played well, give them a Saturday off.
9. Win the game of life. Winning is important but realize most of these kids won't be playing at the next level so it is important to teach the larger life lessons and work skills why playing football. Also, this should got without saying, show the kids, AT ALL LEVELS you care about them more as a student/person than a football player.
10. Create a team culture, remind ALL players that they play an important role, no matter what that role is, especially the scout team players. They may not perform on Friday night but you have to give those kids a sense of ownership of the victory. They work just as hard as the guys in the field in practice.