I do follow "my" rules/guidelines that are important to me for the look/product that I want - silly little things like having the blocks end up the expected size, seams line up, the top lays flat, no pleats in the backing, etc.
Usually by having tried to do some "shortcut" that just made more work for myself in the longer run.
The "rule" I hardly ever follow:
To use starch or sizing on the fabric before cutting it. (Except when working with a lot of bias cut pieces)
I have this idea that fabric should be robust and stable enough to not need it.