Did you read first Apple design guidelines ?
A good way to learn is to look at other apps, not to copy but to ask each time the question: what makes it pleasant to use, what is great in this view… And a last thing: keep it simple, don't try to add fancy features just for the sake of it.
in addition to Claude31's suggestions, i'd recommend looking at Mark Moeykens's (Big Mountain Studios) "Itinerary App Course" on YouTube. he has several parts early in the series talking directly about design issues (colors, fonts, icons, look-and-feel), and often comes back during the series to look at custom design issues for UITableView cells, buttons, and so forth.
hope that helps,
Not all devs have those skills too, so don't feel bad.
You could hire someone to design it for you, but not all devs have that type of budget, but wait...it doesn't take a budget to put your app in front of users and get their feedback, working step/by/step to incorporate their ideas, keeping in mind that process is basically iterative, so expect to learn things about your app as you go, just be flexible as you follow where that leads. Don't be surprised if it results in an entirely new type of app, etc.
About icons, tho, those -may- be worth paying someone else to design if you can't manage to whip up something clean/attractive.
About what you can read...start here for help from the mothership: View Design Resources
In addition to Claud31 and KMT's answers here are my 2 cents:
- Read the Human Interface Guidelines. You would be suprised how many developers have not used the HIG. It gives you a great point of reference and you'll learn some design language. This can make it much easier to work with designers and other teams.
- Learn a design tool to make mockups. I prefer Sketch or Keynote which Apple provides some great design resources for. Sketch also has amazing online tutorials and documentation.
- It is worth checking out WWDC design talks. My personal favorite is Iterative UI Design where they build a whole app using keynote. This definitely got me thinking differently and more curious about the design side of development.
Hope that helps and good luck!
Just another point: good design is not only graphic design. It has a lot to do with what we could call "mental" design. Is the app logic easy to follow ? Is it easy for user to find immediately where he/she should tap on screen, to get what type of result. And of course allow for mistakes to be without any bad consequence.
The point here is that developer is the worst placed to evaluate this. As we know perfectly how the wapp works, it is impossible to imagine where a new user may get lost. As KMT stated, best is to ask genuine testers to paly with the app, and if possible observe when they hesitate, mistake…