philosophy and psychology first. these will potentially help you develop non-stereotypical thoughts and conclusions. This will help you to observe and record information in a nonjudgmental, objective manner, as well as allowing for a compassionate understanding of ideas that differ from your own.
Well, it depends on what you mean by "developed". You can be "an expert" and read/study all material on a specific topic ... or you can be "well rounded" and read/study material on a variety of topics.