Generally as you are the only person who sees your notes, you are the only person who needs to understand them. If you can write in a form of shorthand to save time, and prevent the early onset of carpal tunnel syndrome, then by all means go for it. There is no one correct way to take notes, the fastest way depends on the source that notes are being taken from and the note takers personal style. As long as you keep a few basic tenants in mind your notes should do fine. Like everything else in history, note taking is a skill that can only be acquired with practice.
- If you write down everything in the book says then your wasting rather then saving time
Don't just regurgitate what the book says. While the authors thoughts are apparently important enough to warrant being noted down, your essay in question is about YOUR thoughts are on the matter. If you don't write down your critical interpretations of what the author has said, then your likely to have forgotten them by the time you get around to writing your essay.
- You need to be able to tell where your notes came from
Otherwise you won't be able to cite anything you have taken notes on. Remember to include the relevant page numbers so you that you have that information handy when using your notes for the purposes of writing your essay.
- If you quote something make sure you know its a quote
If you insert a quotation into your essay later without a proper citation then you are guilty of plagiarism and your essay will be given a failing grade. This is true even if you write a quotation in your notes and then innocently forget to cite it as such when you reproduce it in your essay. It takes roughly two seconds of work to place quotation marks around any quotes in your notes and prevent this from happening in the first place.