If you are under 18, check out the local 4-H clubs or Pony Clubs. Otherwise, try to find a riding club in your area & get involved. There could be a club that puts on the horse shows or maintains the trails. Whatever discipline you are interested in, there is probably a club locally that would welcome you.
You guys could all arrange to do some kind of fun show with the horses there.
Get really into it and invite everyone who goes to the barn. Could be really fun and would give every one somehing to look forward to