I don't really use the cards, though I know that many top screenwriters do - including John August. (He wrote an additional post about card tips here.) It can be a great way to look at the structure of your script in a visual way, and also a way to force yourself to think about the necessity and movement of scenes. But it can also be a colossal procrastinating tool that isn't all that different from an outline or beat sheet. And for what it's worth, I think Final Draft has a card feature that simulates the visual layout.
Everybody has his or her own process. The important part is creating a solid outline and figuring everything out before you start writing.
Steven continues: Another thing my professor mentioned was that we should avoid using the word "we" when discussing action in a script such as "we then see the red car approaching the house" or "we get a sense of terror when seeing the hook wedged into the door knob." I'm a little confused after reading a few professional scripts which have used "we" when describing action. Is this something I should avoid doing?
Some teachers will tell you that the "we" is an absolute no-no, but like you discovered, some pros do use it. I think the key is to use it sparingly. Sometimes it can help the reader see how the camera will move, but sometimes it gets annoying. If you can figure out a way to write your description without the "we," I'd recommend going that route. That way, you won't annoy the people who despise it.