The only thing I can imagine would be relevant is that I'm using pfn's android-sdk-plugin.[1] I also have a sort of generic build.scala file I tend to reuse for Android projects (it's based partly on Ascension's, but has been tweaked a bit), which may also be useful.[2] I leave most of the proguard configuration up to pfn's sbt plugin since it does an acceptable job, but your mileage may vary.
If you don't need the sbt build system for your project, it's pretty simple to get started. Here's my guide (and some code examples) for using just proguard + Intellij. Using sbt isn't difficult to set up either, though I consider it a bit overkill for smaller projects/scripting.
[1]: https://github.com/pfn/android-sdk-plugin/
[2]: https://gist.github.com/nilium/db5bfac2174370ebdd97