Establishing the most foundational rule of hermeneutics is a bit like choosing your favorite child. The reality is that exegesis is a combination of methods to arrive at the best exposition of the true meaning of a passage. These methods include a variety of principles or rules, some of which are justified by the internal claims of the Bible itself, and some of which are justified by applying the God-given common sense that we have.
Having said that, the primary aim of hermeneutics is to objectively examine a passage to uncover the truth proposition that it is making. Therefore, I'd assert that a primary principle for the hermeneutical endeavor is to strip away a majority of the biases with which we approach a text (which I just did today and was called out on itwhich I just did today and was called out on it) and attempt to discover the timeless truth that exists in the mind of God that he has chosen to reveal to us. Under that is an umbrella of tools and principles which we could delineate and prioritize, I guess.
Having said that, hermeneutics is a method developed by people to do this very task much like the scientific method is a way discover and describe the nature of something. I'd stop short of saying it is a God-ordained activity and so there's no real mandate to be biblical scholars - just to teach, observe, and witness. Hermeneutics is a way to support these mandates with some solid fact-finding and application.
