1. Have a clear focus
Unlike the desktop browser world, the mobile world is task driven. The mobile context means that your users are likely multi-tasking and are looking to an app when they have a few minutes to spare to and want to accomplish something very specific. Your app needs to have a clear purpose and emphasize the most current content/information. Given the screen real-estate constraints it's important to approach app design by asking:
What's needed right now? - based on the purpose of your app, the most relevant and timely information should be the most prominent. i.e. Breaking News, current weather conditions
Is this needed at all? - the most difficult decision is not what you include but what you don't include in your app. It's more important to create an app that helps the use achieve one primary goal really well than be functionality rich.
2. Make it work like I think it should
Your app should be intuitive. If it requires help text or instructions to use, it's time to go back to the drawing board. The main function of the app should be obvious. A great example is the native stop watch or compass app that comes with the iPhone. It's pretty clear by looking at the app what it does and how to work it. The physicality aspect of the compass helps make it intuitive. It looks like a compass, you physically turn your phone like you would an actual compass to get a reading. It's simple and intuitive. And the graphics are fantastic to look at.
3. It's not about youAlong the lines of creating user-centric apps, don't crowd the already precious real-estate with your logos or anything not relevant to the user achieving a goal. Your marketing and branding opportunity comes with designing your app launch icon and in crafting an effective app store description.
4. Make it seamless
Apps that are mobile variations to a wired web browser based parent should have seamless connection with the data available. Don't require a cumbersome app set up process, leverage what you already know to create a ready to use app moments after app store download. In today's social media world, people like to share for better and worse. Encourage collaboration and make it easy for users to tell their friends about your app and share content.
5. I want to find, I don't want to browseThe mobile context is all about relevant information ready before I know I need it. The search capabilities should be tailored to fast and rewarding searches. Display partial results quickly and use on-screen controls to help users quickly filter through results sets. There are out of the box user interface elements called scope bars that can help with limiting the data that an app pulls back. Tap into the phone senses such as the GPS to order results by those "closest" to where the user is now. And keep the search box near the top or header of the app where users expect it to be.
6. Entertain me
Creating a truly enjoyable experience relies on not only a focused, user-centric purpose but also stunning graphics and the use of physicality and realism. Enhancing a user's sense of direct manipulation such as turning pages or physically rotating a phone to engage the compass creates apps that are delightful to use. They can make performing the simplest of tasks a truly memorable experience. And help create the buzz that you are looking for.
There you have it. 6 golden rules for designing iPhone apps that will have your users coming back for more and spreading the good word about your app. Read the Part 1 of my blog series on Decoding Apple's Human Interface Guidelines here.
Use the comments below to tell me more about the apps you love and which apps keep you coming back for more.