Making an app successful requires two distinct skill sets including:
1. product development: UI/UX, Graphics, clean code and all that stuff
2. marketing: Tricky business. How do you monteize? Work with Carriers? Pre-load your app? Promote it through blogs? Get good reviews? Create a hype in social media? Paid vs. Free? What kind of in-app purchases? Which ad network and what marketing partners to use etc. etc.?
I have seen many apps on app store that have the ability to be sell like hot cakes but they get dumped under the piles of bad apps which are being marketed properly.
If you guys think that you have an app that have the nice concept, good design and ability to be successful, but it is lacking marketing muscle, please send me a message. I will analyze your app and provide you free advise on what is it lacking. If I find that I can help you making it successful, I will let you know and we can discuss these details more once the key issues are identified.