My advice is to look at the athletes that will be there. Pick a few that you really want to get their autograph. Get there when the park opens and grab the pamphlet with the event times. When you see the athlete is scheduled to appear on the stage beneath the sorcerer's hat make your way there. They athlete's are driven to the stage via car. Make sure to stand right by where they park the cars. The athletes will usually sign autographs after they are done on stage and before they get into the cars. Other than that you can try to find them in the park or at any of the other events, but I believe the stage is the best place to get them.