The best way to study is to break down the content, analyzing every detail until you have a full understanding of the components. Only then should you follow with reading, re-writing and summarizing. Memorizing alone may be enough to pass a test, but the whole point of the subject material being delivered, is for you to acquire an understanding. But you should not only aim to acquire just an understanding; One should instead aim to find flaws in that particular subject and present the required amount of justification necessary.
This is the way I now study. My average grade over the last year with Tertiary Study being: 95%
As for high school, I had no technique and I would just try and memorize, if doing any study at all. My results were poor, but there were some other contribution factors to go with that, like family issues having a large impact om me.