3. Design Principles

The Worldwide Developers' Conference for 2017 at Apple has a link to an hour-long video on 'Essential Design Principles' that does an excellent job of covering these.

I would highly recommend that project facilitators, product supervisors and other interested people make a point of seeing the WWDC video session ‘Essential Design Principles’ in its entirety.

If you are new to development or product design, I’d say this video is mandatory.

This talk is a really good overview of the most important design principles used in conceiving, planning, and executing a given design, be it for mobile, desktop, web, or any other interface of the day. It also provides an easy-to-understand set of practical guidelines that anyone writing software should keep in mind and refer to when creating.

The video is available here. https://developer.apple.com/videos/play/wwdc2017/802/

Another video from WWDC 2016 (among several; I encourage you to seek these out) covers the important related topic of making your app engaging and useful to everyone, including those with accessibility challenges. Accessibility is a huge topic in itself, but this second video gives some very useful points and issues to consider in thinking about your app.

https://developer.apple.com/videos/play/wwdc2016/801/

Viewing these videos requires registration of an Apple Developer account first, but the good news is, these can be had for free; payment is only charged when you as the developer are ready to distribute your works on the App Store.