Screenshots are a great start.

Close second is formatting: I really like projects that start with the hook (usually an image of the software in use or an "elevator pitch" of what it's trying to solve), follows up with a list of features, capabilities or FAQ, and then finishes with the less salient info like contribution instructions, build instructions, and general how-tos.

I think upfront it's worth noting that you probably don't need people to "keep on reading" your entire README, in an ideal world you're able to convey the important details first and address more granular issues in a structured and easy-to-parse way. YMMV, but that's my two cents.