The iOs app icon is your very first visual contact with the user. Wherever he finds an application in the top, in the search, by clicking on the AppStore, first he will pay attention to the application icon. And often it depends on her whether he goes past or to the page with details.
It follows two simple rules. I will try to demonstrate them with illustrative examples.

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The first rule: the icon should be beautiful
I will not argue that the beauty of the icon is a subjective concept, but the icon must be of high quality. If the icon is slapped somehow on the knee, the user will expect the same from the application.
Should we expect an excellent interface and functionality from applications with such icons?

And with such?

Make a beautiful icon is very simple, just hire a designer :) and keep track of good applications in the AppStore.
The second rule: the icon should stand out
Take a look at a small sample of the paid Social Networking top:

When I look at it in my head the letters WTF pulsate ?! :) How should the user choose from this variety? Where is the application for audio, where is the video, where is the faster client?
What if you put yourself all five, how to distinguish one application from another on the iPhone screen?
If you want your application to download -
stand out . Stand out in your category, stand out in the general top.
Unlike beauty icons, the second rule is very simple to check. Take your future icon and “try on” it in the top you need categories in the general top and on the iTunes screen. Experiment with color and shape until the icon becomes the most visible.
It is not difficult to do these operations with our hands, but we have made an
icon testing tool for ourselves. It works easier than simple: load the future icon, select the country, category, and get four pictures. The results of experiments are easy to share with colleagues or customers.
A small summary: in order to increase the conversion of downloads of the application and the activity of its use, the icon should be beautiful and stand out among other applications.Good luck with the applications and more good icons! ;)
Btw. We
are looking for C # developers to create high-quality mobile applications.
UPD. And show your icons, if any. </ B.