Creating an iOS icon is either one of the most rewarding parts of creating an iOS application or the most daunting, depending on how good you are with graphics. Luckily, there are a lot of tools out there now that make creating a great icon easy.
You're going to need four tools to start:
- iOS Icon Template
- Common sense
- Decent color choices
Photoshop and the iOS Icon Template (created by Michael Flarup) is a match made in heaven. While creating an icon in another designer is not hard, Michael has made it incredibly easy due to the fact that you design the single icon and his template will scale and and transform it into all of the necessary sizes for iOS. There are currently 15 icons sizes you need to create for iOS. It's an absolute nightmare if you have to do them by hand. Save yourself and use a template like this one - I can't recommend it enough.
Once you've booted up Photoshop and loaded up the iOS Icon Template it's time to start designing. I won't go through actually rendering it in Photoshop since that process is discussed on the AppIconTemplate.com site but I do what to touch on what you need to do to create a good looking icon.
As I mentioned above, you need common sense. Common sense is remembering "oh, while I design this icon, I should remember that it's going to shrink to a smaller size" or "I want my icon to stand out but I don't want to alienate it by choosing wild colors or not sticking to the iOS flat theme". Here are two common sense tips that will save you time and embarassment.
Do not use words in your icon! A letter, ok, but not a word! Words may look good at a large resolution but become unreadible quickly when the icon shinks! Avoid words at all costs.
Do not ignore the iOS flat theme! Your app will stand out in a bad way if you choose to ignore this and go for some other design type. Flat is in for iOS 7. You can, of course, take liberties with what that means, but keep it within reason.
Finally, make the right color choices. It's easy to get overwhelmed and want to throw a log of color into the icon to make it stand out. Resist the temptation! I find that the really beautiful icons are simple in their design and color choices. Almost to the point where it makes you think "wow, they paid some designer just for that?" Here's a tip to make yours look as good as theirs:
Do not use more than 4 colors! If you know what you're doing, ignore this. But for everyone else who doesn't have a strong artistic background, or color theory for that matter, should stick to four or less. Any more and the icon gets noisy with activity. I strive for 3 or less. It helps reinforce the point above, keeping with the flat theme, as well as helps keep the design simple. Check out Color Matters for more ideas of how to combine colors. Take a look at "analogous" and "complementary" colors. The former is awesome for icons that are calming since all the colors are closely related. The latter is excellent for making one portion of your icon pop with color!
Here's quickly thrown together example I created for a new application I am designing having to do with bug tracking. Notice how it is only 3 colors: white, purple, and dark purple. The shadow is not a typical feature in flat design but I enjoy playing around with different techniques and I think it gives it that one "feature" that helps the icon standout from the others.