How do you improve in sports?

That depends whether you are talking about professional sports, high school sports, College Sports, or recreational sports for younger kids.

If it is for professional sports, the best way would be to advertise on TV. For high schools, place posters and banners all around the school stating tryout times and other important information. For college sports, do the same as in high school or send messages about the sport to local high schools. For recreational sports for younger kids, post tryouts or how to participate in the sport around the neighborhood like at local parks.