Despite being a book primarily about designing for the Internet, Steve Krug’s “Don’t Make Me Think” makes a point to address what usability considerations exist in the world of mobile app design. The gist of the message is that everything we know about usability for desktop devices applies to mobile devices, but that making mistakes in a few key areas can have even worse consequences when the device’s screen is 4″ and not 15″. To summarize these key areas in a word: Mobile design hinges on discoverability.
As Krug points out, tradeoffs must be made in mobile design. Not every piece of functionality can be displayed front and center while keeping text readable, so affordances must intentionally be hidden and continuously opened by a user to be… used. Bad mobile design means hiding these affordances badly.
“What can I do with this application?” “How do I access my X?”
*Repeatedly taps, long presses, swipes, and pinches until something happens on screen*
When it comes to avoiding this scenario and being good at promoting discoverability, my advice is to follow conventions. Use carets to denote sub-content, hamburgers icons for menus, make swipeable views noticeably swipeable with scrolling indicators, etc.
Users understand that mobile design can suck, so they’ve developed conceptual models that focus on conventional UI elements made for smalls screens. Use those elements!