Getting teammates to play support in any game is tough, and League of Legends is no exception. Part of the issue is that support doesn't always seem as glamorous as other roles. And part of that, too, is that players often need to learn how to think about the game differently.
Here's a splendid guide by Cloth5DotCom that looks at champions, appropriate techniques, and playstyles that you can adopt as a support, all presented in clear and simple language. It's worth watching—and hopefully, it helps you (and your team) play better!
Supporting in Team Fights - impaKt Support Guides [Cloth5DotCom]