A good resource for inspiration is www.designprinciplesftw.com, which claims to be the largest collection of design principles on the web. Because of its size, they've also implemented an "I'm feeling lucky" interface where you get a random design principle everytime you refresh the page. That can be found here: https://www.randomdesignprinciple.com/. A good way to find interesting or dull design principles would be to generate some random ones and then checkout the full set of principles to understand the team's approach better.
Personally, I think a "good" design principle has a broad application to many areas of design and is described by an easy-to-understand yet memorable word or phrase.
Having a design principle called "Smooth" is broad enough to be a guiding star for motion design, onboarding design, etc. but it's not immediately understandable and isn't very memorable either.
Or take this one from Microsoft's Bing team: "Enhance, don't hinder search". It has a somewhat limited scope, it's fairly understandable at first glance, but I personally don't find it memorable.
On the other hand, a design principle called "Build for Grandma" is broad, catchy, and intuitively meaningful.
Since design principles are very much crafted for their own unique context and audience, I suggest you try to nail down a design principle approach that appeals to you best. Trying to find the right words isn't going to be as instructive. Who knows, maybe my first two examples are perfectly suited for the product and the team they are targeting.