I've been searching Google for hours, and it just keeps coming up with useless results of other peoples .design
files when I want to learn how to create an application bar icon from scratch, not using their .design
files. So, how do I do it?
The guidelines are listed in MSDN. As an addition: Use PNG, transparent background and white foreground for the final image to let the system invert your icon for the light system theme.
I would recommand to use the basecircle file from C:\Program Files (x86)\Microsoft SDKs\Windows Phone\v7.1\Icons\dark as a little help to set the optimum position of your icon. The circle itself is drawn by the system.