No thank you
Turning down things not worth your time is a great way to safeguard your time, so that you have time to spend on things more worthy of it.
It's also something most people find particularly difficult to do. Not necessarily because there's a real risk involved (there's not), but because we often don't know what to say and what not to.
Hence the appeal of How to Say No, a directory of templates for email and text exchanges designed to help you do just that.
Because saying no doesn't have to be a hassle. And saving time for the most important things shouldn't be.