Website design falls under broad categories: content and optimization. First, your content would need to be very compelling yet not repulsing (cancers shown in progressed stages can be more repulsive than compelling or persuasive). One positive, up-beat tract to take is to have testimonies from teens of all manner of ethnic backgrounds who give energetic, happy, optimistically persuasive testimonies of having quit or of having successfully avoided smoking. Song and dance by these same successful and productive role models is very persuasive.
On the backside, optimization level, you need to know how use the information portals available to bring your website to top ratings through proven placements and techniques. There are online workshops to teach SEO and beyond (including YouTube placement) optimization.