Tagabek,

This is a very complicated question to answer for most app developers. We have been trying to discover the answer to this very question in the facebook group for app entrepreneurs and marketers - https://www.facebook.com/groups/appentrepreneurs/

One thing which has consistently stood out is that create an app which stands out. Learn marketing and build a network of apps. The finer details on app marketing are probably beyond the scope of this post.