Check out the category on Robert's Rules, Bylaws and Legal. You'll find tons of info in that area.
Some PTO's operate under the umbrella of the school, some kind of fly on their own, and some go the "official" route of becoming an IRS recognized 501c3 non-profit organization. All can work-it kind of depends on the goals of your group and what's the best fit for you. Your school's expectations of your group's role can also influence how you operate.