This does not guarantee you to become an NBA player. However it will help. First off, if your under six feet tall it is going to be about 10x harder for you to become an NBA player. Size matters a lot. You can't be too fat or too thin. You can't be too short or too weak. If you are small its not impossible but its going to be harder. Basketball athletes need to be fast and big. So you will need to work on being fast and building muscle. You will have to play almost every chance you get. Grades need to come first though. If you don't have good grades you can't play high school or college, and you might not graduate high school which is a requirement for the NBA. You will need to try to make the high school team. You may also want to play for travels teams, and super league teams. You just want your name to get out there. Then if you are good enough you should be able to make a college team or even get a scholarship. If you don't get a scholarship you still can tryout for the team. David Stockton didn't get a single college offer and after his freshman year he got a full ride to Gonzaga. He then made the NBA as a member of the Sacramento Kings. After college you should enter the NBA Draft. Even if you don't get drafted you can still play in the d-league or over seas and eventually make the NBA.
you can find great workouts to help you here