I try to rely on principles rather than rules. To me the distinction depends on the difference between a goal I'm trying to achieve and a clearly defined prescription for behavior. This is something of a situationalist perspective: a principle guides, but does not bind, for the boundary cases where the proper path is not clear. By contrast a rule is a rule; it is to be followed.
As example we might contrast the Judeo-Christian rule: "Thou shalt not kill" with the principle (Buddhist, perhaps) of preserving life. The rule is clear cut: but what do you do in the rare (but much discussed) situation where your ability to take the life of one person will save the lives of many others? The rule is simple, clear cut. It does, however, put aside the difficult conflicting values in the problem. The principle is conflicted; judgment is left in the hands of the individual. It is more difficult to apply a principle in this kind of case than a rule--or at least the decision is more difficult.
Yesterday I was writing about structure and the structure of the Introduction. I got a question about the structure that said "...are we expected to...". I know I'm kind of misreading this, because the questioner, I think, is not looking at me as an authority figure who sets expectations that must be met (I hope). But it made me think about structure, formulas and why we use structures and formulas.
Part of what I wanted to show, in addition to suggesting a specific sort of structure, was that structure is motivated. The formula is not there simply as a formalism to be followed, but rather the formula is there because the writer has some purposes, and the formula helps the writer accomplish that purpose.
One purpose that all writers share is the desire to get the reader engaged. Hence there is an introduction of some sort. In fiction, writers introduce there work in ways that set up tension, or that address the reader; the reader of fiction has certain expectations, and the writer is going to play with those expectations. In academic writing the introduction is done differently: the academic writer wants to put all the cards on the table--or at least the most important one; he academic writer draws the academic reader in by convincing the reader that the work addresses a significant issue, and that the work is done well. What happens if the academic reader thinks the study deals with an insignificant issue, or the research was executed in a such a shoddy manner as to be worthless?
The point of structural formulas is that they help us engage the reader. The models have been used because they work, but they have also been used because they suit the writer's purpose. If you can see structure as a tool to help you reach the reader and convince the reader of the quality of your work, then you will deal with structural formulas in a different fashion: you will see them as suggestions that may help you act in accordance with a guiding principle (like the desire to engage the reader), rather than onerous prescriptions.