General guidelines for creating my own ringtones?

I thought about submitting this to r/android, but that seems like a real high volume subreddit, so I apologize if this isn't the right place.

My N4 arrives tomorrow and I'm ready to start creating my own custom ringtones. I'm familiar enough with Audacity to be able to do some basic audio editing and create mp3 clips. Are there any general guidelines on bitrate/sample rate for ringtones? Anything else I need to know?

I've created a few for my iPhone in m4a format and it wasn't too difficult.