Combination of instinct and reading material. I feel more informed as a parent when I read. There are tons of things I've learned and have applied and found extremely beneficial to our relationship. I don't necessarily understand the "i'll just do what my parents did" when there is so much more about development known today. Why is it that we accept being educated on everything else in life but when it comes to our children, some believe they can do no wrong and need to learn nothing, it will all come from instinct. Yes, a lot of it does, and are instinct can also tells us when a great book has a paragraph you would never apply also. I guess i find that attitude as some what ignorant and closed to growth/learning/being educated to IMPROVE on what we already have.
I subscribed more to Sears and the Positive Discipline theory (Lisa Faber, etc). Then since I have boys I found books like Raising Cain (just got this one), Real boys (Pollack, LOVE this book), Gurian's book about helping boys in school (can't remember the title now). Oh, also, found this book called ScreamFree parenting and LOVED it! It has SO much good stuff in it (and no it doesn't only speak of not screaming it's a LOT more then that).
I don't care for Dobson or really most traditional, conservative christian authors for parenting or relationship advice though.