I don't use my phone as much as you do.
This is something my dad told me a couple times as I was teaching him a few features of iOS.
If you read this, you probably know more about iOS and technology in general than the average person. Many things that are easy and obvious to us aren't to most people.
The following are a few observations I've made over the past couple of years. I don't have numbers, but I'm pretty sure my usage of 'some people' should be more like 'most people'.
Some people don't use their phone extensively
For most people, a phone is just a tool to communicate and get entertained when they have time to kill. Because it's not an object of real interest to them, they don't have or take the time to learn new flows, icons, terms or read manuals (nobody reads manuals).
My dad often touches his iPhone's screen inadvertently; that brings the current app to another view/state and he's lost.
Some people hesitate to try when they don't know the outcome
People are not adventurous by nature. On a computer they're afraid to break everything if they try something. They approach phones the same way, and if an icon is unclear or a label confusing, they won't touch it.
Some people don't know the difference between similar technologies
What's the difference between WiFi and 3G/LTE? To most people those are the same, they're the Internet. As long as they are connected to the web they're fine, how they are connected, they don't care.
Some complain the Internet is too slow on their iPhone, they don't notice the 'E' next to the carrier's name, they don't even know what that 'E' means.
What's the difference between SMS and iMessage? The fact that it's combined in the same discussion is convenient, but many people wonder why they have blue and green bubbles.
Some people don't care about aesthetics
In the Talk Show's 56th episode, John and Guy mention several people they showed iOS 7 didn't notice the visual difference with iOS 6.
The phone is a tool, and people want to get things done with it. Take a unit converter app for example. Everyone want that kind of app on their phone because it's convenient and can be useful sometimes. You spend hundreds of hours building the most beautiful unit converter app and charge $1.99 for it. It doesn't sell because people prefer the ugly free competitor. To them both apps do the same job, but they choose the free one because they don't care as much about aesthetics as they do about price.
Use words carefully
I know it's annoying for most developers, but spending time to find the proper terms and sentences is very important if you want to avoid confusion. Avoid nerdy terms but be precise when it is necessary.
The iPhone's manual used to be a great example. Big images, a few lines of text to explain all the main concepts and features. Sadly, nobody reads manuals and the iPhone 5S doesn't ship with one anymore.
Stay close to Apple's default behaviors and visuals
People are used to the default interface, if you try to differentiate your app too much, people will be lost. Icon for a delete action? Use a trash, not a cross. Back/Close button? Put it in the top left corner of the screen because that's where it belongs on iOS.
iOS 7 is a big change and some developers are tempted to put borders around buttons or backgrounds to keep a button shape. But iOS users will get used to that new design, and quicker than you'd think because the apps they use the most are Apple's, like Mail, Phone and Messages.
Spend time observing Apple's apps, their flows, animations, and text. They're not always perfect, but most of the time they solves problems the right way. And it's a great source of inspiration.
Provide some help within your app
Whether it's a walkthrough when the user launches the app for the first time, an overlay, a sample document or an embedded help web page, your app must provide some help for the user. And it has to be easily accessible, people won't find it if they have to dig into a long view hierarchy.
It's usually not a fun thing to work on, but you can make it cool, the perfect example being StatusBoard for iPad by Panic. The guide looks like a real manual, and it's actually entertaining to experience the first time you launch the app.
The tip of the iceberg
I just scratched the surface here, there's a ton more to say about improving the user experience for mass market apps.
We spend our days working on apps, we talk about development, technology all the time between ourselves. But sometimes we need to take a step back, and think about the guys who are not in our bubble. They are the majority, we are the aliens.
Many things in technology are obvious to us, but not to most people. We have to take that into account while we build products.
This post is based on a presentation I made at CocoaHeads Montreal on October 8th, 2013. You can view the slides here.