This could be:

Just don't invent them. As designers, we already have a rich palette of existing controls to choose from. If you're thinking about making a new UI control, please stop and think about how hard it will be for users to learn yet another interface pattern. I promise you this—there's already a way to do what you want to do.

However, every now and thn, something new comes along that is genuinely an advance in UI. Back in 2008, Loren Brichter made a Twitter app called Tweetie, with a unique pull-to-refresh interaction. Pulling the view down would show "release to refresh" and releasing would show a spinner. The pull-to-refresh interaction went on to be included in Twitter, which bought Tweetie, and then in iOS and Android apps in their hundreds.

So, don't invent new control… unless they're astonishingly good.