App icon is more important than it's name.

What icon represent, and why its so important.  

Icons is your business cards, when some one in the Appstore search for specific application by keywords, your icons stand shoulder to shoulder to other icons. 

So you must pay more attention to the icon design and don't just make it an image you found in the internet (of course if its good image, you can use it anyway)

Main principles in designing them 

in App store designer have some best practices in designing icons 

• Take a snap from the application itself and make it the icon

• you can make the icon as a small part of your screen, if your screen is designed well, and have something special about your app.

• When to use text 
• if the application designed for a big brand, its fine to just add the text of this brand, like mobil and microsoft

• And what about letters
• they dont use just letters unless its known also for a big brand like the white F of Facebook and S for skype

• No details
• icons must reveal something about your app, not many details but any insights about the app main function
• your icon may be a visual description of your app function, interface, name or its brand as well
• Watch out for the "visual addiction" 
• make your icon fun, make it colorful, make it memorable but whatever you do don't make it mysterious 
• done be over concerned with the visual metaphors and remember. more commerce, less art.

SO, don't underestimate your icon design, invest more time and polish it well, and if you face some problems in designing. or you don't have the icon design skill. consider hiring a designer. it will pay for itself.

Salam,

M.Aleem