There's nothing more boring and ineffective than generalities. Interesting, convincing writing is specific. Instead of writing "Last year in one of my classes...", write "For example, I found myself in a predicament during a review session in Pre-calculus when...".
Here's a great example of how to continue to drill down from general to more and more specific. Try to do this every time you're about to write a supporting sentence in one of your SAT essay body paragraphs.