Having a "good eye" and knowing what looks nice is good, but if you don't have that initial "vision" then you will be spending a lot of time playing around until you stumble on the design that looks good and even then you may never reach that point.
As developers, we are very good at following the guidelines put down by Apple and making sure that we follow those - after all it's a nice logical set of rules to follow and that's exactly what we do when we write code - follow logical rules.
Unfortunately the design side of things doesn't have rules that we can follow. Yes, we may be technical at using Photoshop or some other drawing application, but when it comes to actually having that spark of inspiration, that's not something we can just click a button for.
Looking at other applications is one way to go. But then you may end up having an app that looks like another app or a collection of a number of apps and then you may have problems with a fluid user interaction.
My own approach to this problem was to go out and find someone who is really good at doing that art stuff and working with them. I struggled for a long time designing my own stuff, but looking back, it was obvious it was a developer (me) doing the design. I'm not sure what it is, but there's an extra something that these graphic artists seem to be able to do that I just can't get and that makes all the difference.
But the flip side to this is that he can't code. Sometimes it's best to just stick to what you're best at.