Post release maintenance
Your app may be in the Apple's App Store, but there is still plenty you can do to improve your users' experience, as well as the app itself.
Support
Good after sales support is as important as good code to the success of your app, never more so than in the period immediately following its initial release. Try to make as much use as possible of the resources at your disposal, including your support website and social media. The exact way in which you do this will vary hugely according to the nature of your app and the type of user you expect to be engaging with it.
Think twice, however, about making your site or social media pages open to comments from users. One disgruntled user can do a huge amount of damage, even while a thousand contented customers quietly use your app every day.
Direct feedback can, however, prove extremely useful in identifying the areas of your app that could use improvement, or that are not working as you intended them to. It is worth considering...