Hey guys,
are there any style guides for app development out there? As a backend developer I do not have much experience on how to position UI elements so that it looks harmonic and natural. So what I am looking for is basically some sort of a "best practices book", with design/UI problems and possible solutions to it. Can you guys recommend anything?

Jquery Mobile haha

Difficult - UX decisions (which is what you're asking about here) are, in my experience, very context-sensitive. You need to consider what you want best practice advice for - e.g. a dashboard, forms/data capture, menus, etc.

I don't want to completely ignore your question, but there are abstract books on the concepts (and psychology) of UX design and then things tend to get a bit more specific to the context. Not sure there is a one-size-fits-all book for that.

I see what you mean. I just thought that there are maybe some books out there that give you examples why certain user interfaces are good or bad.

Currently I feel a little bit lost when trying to create a nice looking interface, as I am always questioning my decisions. Should I use a list or radio buttons? Do the colors that i am using for background an foreground harmonize?...

It would help me a lot if there to have a list with "do's and dont's" that helps me in my decision making. e.q: "Usually a list is used when...". or "It makes more sense to use radio buttons when..."

ios styleguide
https://developer.apple.com/ios/...

google material design for android
https://developer.android.com/desig...