Seriously, designing app mockups for iOS is scary as hell. Everytime I try to do an iOS mockup, I keep thinking of those "rules" in the Apple Human Interface Guidelines that says you can't do this this this, and that thing must be so and so color etc.
Say, if we try something like this :
Is this ok? Or must all iOS apps have a white background, buttons must not have borders, use only the standard iOS controls etc.?
The Apple Human Interface Guidelines are 'Guidelines', not 'rules' - you don't have to follow them entirely, design and build what you like.
Guidelines are guidelines.
If you follow the guidelines, you are leveraging the platform's consistency. This reduces the cognitive load for your users because they already have an innate understanding of how to use your app, and because your app is more likely to feel like it fits along with everything else on their phone.
If you choose not to follow the guidelines, be able to clearly articulate why you're not following them. "I don't want to" is probably not a good reason. Keep your user's experience first and foremost in your mind. After all, the guidelines are for general app development, and they don't necessarily make sense for every application or every workflow. Any app should be user tested; this is more important the further that you get from the guidelines. If users aren't able to find an important control because you've chosen not to use the system controls, you might need to re-think some aspects of your design. If you have a well-articulated case for why the guidelines don't fit, and if you have data from user tests to back up breaking the guidelines, your boss and clients are going to be a lot more comfortable.
There are many reasons for an app to get rejected by the App Store. They're often easy to fix. Don't treat a rejection from the App Store like it's the end of the world. Accept that it's a possibility, and be responsive to it if it does happen. Don't waste your time worrying about it happening. Spend your time on creating and testing an awesome user experience.
Look at pttrns.com and see how visually rich existing apps already are. You may think of the human interface guidelines as suggestions for what to do when you don't already have a solution in mind. It's one thing to ignore the HIG because of being unfamiliar with it, and another matter entirely of consciously choosing to do something differently than the guidelines suggest.
These are guidelines and no more or less than that.
Saying that, the company I worked for have quite a few apps in the app store and we we recently got some of them critiqued by Apple due to wanting to be featured in a particular app store.
Out of this, they flagged up many issues regarding UX and also commented on us not using their guidelines as much as we should have. I found this very interesting as internally we thought we had a great app which did still have some elements of iOS guidelines.
So I guess what I am trying to say is:
