The Search Institute, mentioned in the CSLP Teen Manual, has an excellent website that explains child and adolescent development in terms of "developmental assets." It's a good crash course if you don't know much about developmental milestones and how kids develop in various aspects of their lives.
Planning for your program: Determine the length of your program and your budget, incentives/prizes, and offering teens worthwhile activities, programs and resources. Use social media, your website, and flyers/bulletin boards within the library. Create a space in your libraries for teens, even if it's small..