I'm confused at where sequences begin and end and how they exactly fit into scenes. I'm doing a heavy outline right now, and am a bit stuck on this, because I want to do it the right way, the professional way, the best way. So I want to make sure that every scene counts. And according to the many books I've read, if a scene doesn't turn form a positive to a negative, or vice versa, the scene doesn't do anything and should be removed. So is that all there is to it? Should I just be paying attention to the positive negative fluctuations, and when I can identify them, is that how I know where my scene ends? I just get a little confused when locations change, say, from going inside a house to a car.
Honestly, I think this is what happens when a writer follows a guru too literally. Too many books out there try to reduce writing to a mathematical equation. True, there is a structure to screenwriting, and in some cases those elements are fairly rigid. Blake Snyder's checklist of how to break down a film is one of the more useful tools, but following that "Beat Sheet" isn't the only way to write a script.
The same goes for the mandate that every scene should go from a positive to a negative or vice-versa. I agree that every scene should advance the story in some form, but I have to believe there's more to that than keeping track of positive to negative fluctuations.
I'm a little puzzled by your last two statements. Your scenes should end when they reach their climax. Once you've achieved the point of that scene, your objective should be to get out of it as soon as possible. Look at the scene in Back to the Future where Marty gets the critical exposition he'll need once he's stuck in the past. He's with his girlfriend in the town square, talking about their plans for the weekend and his family. They start to kiss, only to be interrupted by the woman soliciting donations to preserve the Clock Tower. In the course of doing so, she reveals important exposition about how that building was struck by lightning 30 years ago.
The thing is, the writers need a way to make sure Marty would remember those details, and in his current mindset, his focus isn't really on what the woman is saying - so they have the woman force a flyer on him, one that has all the information about the Clock Tower. But there still needs to be a reason for him to hold onto it. That's easily accomplished by having the girlfriend say she'll be at her grandmother's. She writes the number on the flyer. Thus, Marty has a reason to hold onto it rather than discard it in the nearest trashcan.
And what happens after all that's accomplished? They kiss, she leaves and the scene ends. The scene had to lay out exposition and give Marty a reason to hold onto it. Once that was done, they got out of it. There's no scene of Marty talking to other people in the town square. He doesn't buy a newspaper, he doesn't have a lingering conversation with his girlfriend about their homework. The scene has done its work and it ends.
Once you've accomplished what you need to, you get out of that scene. If you don't know WHAT exactly you're trying to accomplish in that scene, then you've got bigger problems than not knowing when the scene should end.