I recently posted on how you might think about screen orientation support. This led to possible consideration on how devices are held in the hand(s). Following the theme of adapting your app design to how your app might be used, you might like to take a look at the free Pew Research paper (pdf) into mobile etiquette.
The report shows under what situations people think it’s ok to use their smartphones, what they do on their phones when taking part in a social activity and how this varies by age group.
Depending on your app, the results of this research might help you determine whether your app is likely to be used in particular contexts. Alternatively, you might even target a popular context such ‘Look up information about where you are going or how to get there’ or make other contexts more easily achievable, for example to help ‘Avoid interacting with others who are near you’! Tapping into common end-user etiquette and motivations might be used as a way to improve app use and retention.