Security : Security is one of the main features of a successful mobile app, as users are so much concerned with their data so you need to put strong security in your mobile app.
Offline work : Most apps are only in the online mode. But you must predict a situation where an internet connection is absent. Therefore consider offline mode too.
Regular updates : The truly excellent mobile app needs a regular process of improvement enriches with new features.
Personalization : People love getting opportunities for customisation. So you can offer them flexible features like background colour, fonts etc
Search : Give special attention to your search area. Make sure that it can be easily accessible from the device
Analytics : Pay attention to your mobile Analytics, track your mobile app performance. If any improvement is needed, optimise it timely.
Social media integration : Social media is a great way to share. So make sure that your users can easily share your content and information with the help of social media.