2x per each class per each day in the semester. IE: In Torts on Wed, don't get called on more than 2x. Same goes for Civ Pro... And so on.
2x in one class period is sufficient to offer your worldview, an answer to a question or to ask a question. If you have additional worldviews, a different hypo or more questions, you need to go to the prof and talk to him after class. There are 50-100 people in your section and the class needs to keep moving on. Don't hold it up. If you're called on for Socratic, obviously that is a bit different-- the prof may stay on you for 15 or 30 minutes to talk and answer his questions.
The point is this: Your classmates will get annoyed with you being Mr. Smarty-Pants or That Annoying Guy Who Won't Shut the Heck Up if your hand is always in the air. It's great if you don't care about what other people think of you, but you will be working with or for these people some day, or possibly need a referral. Don't sour your reputation now.
Just use some discretion. Class time isn't personal 1-on-1 time for you and the professor.
I haven't invented this "rule"-- it's just some friendly advice that several upperclassmen and lawyers gave me when I was starting out in the whole law school admissions process when I asked, "What is your advice for surviving law school courses?" I think it makes some sense. Respect the people around you and use office hours if you want to wax philosophic about UCC 2-207 or have multiple questions.