In my studies at Uni, I remember in my Psychology Course our Lecturer went into detail about this subject. We studies personality theory in detail and how your Values, Attitudes and Beliefs are based on this which are dependent on environment, genes etc. Through analysing these, you get to understand your Belief System.
Below are a few websites that are worth looking at for you to question yours. Many have exercises on them and discussion points. I’d be happy to get any feedback and thoughts: