Briefing is pretty much a waste of time. I did leews style, very short briefs compiled from the lexis-nexis briefs and/or canned briefs and a quick skim of the text. After awhile I stopped reading the cases altogether.
After the third week of law school I pretty much stopped reading the casebooks, save for a quick skim in class to see if there was an important point in one of them. Most of the time there wasn't. Cases are rarely tested on law exams. If you do need to know a case for an exam, you'll know and even then you'll only need to know the title of the case and a one sentence summary of the holding.
I have done well at my school despite not putting too much stock in the cases.
Many upperclassmen don't read at all. One of the top editors of our law review doesn't read casebooks anymore.