Same as the person above--I go to ratemyprofessors.com and see if anyone mentions presentations or calling on people and things like that. If there's someone who's registered with RMP, I contact them to ask them about it. It might be weird, and they might think I'm weird, but I don't really have anything to lose.
If I go to the class and see that the professor requires presentations or lots of discussions, I'll probably drop it. I was once enrolled in a math class where the professor said he was going to call on people a lot to solve problems on the board. I dropped it, signed up for another math class and was so much better off there, so I think it was a good decision. The professor never called on anybody, she was nice, the way the classroom was set up didn't make me feel uncomfortable, and it just had a better atmosphere to it overall.