You cannot write as fast as a teacher talks, and trying is what makes people miss the next sentence. So stop writing sentences. Write the words that carry the meaning and throw the rest away.
Same fact. Nine words instead of eleven, and half the writing.
Three habits that do most of it
Drop the small words.the, of, a, was, because — you will put them back in your head automatically when you read it.
Use arrows and symbols. → for "leads to", ↑ for "increases", = for "is", ≠ for "is not".
Abbreviate anything you write twice. First time write photosynthesis, after that write psyn.
Four words and two symbols.
Short does not mean vague. "Fr Rev 1789 ← food shortages" still carries a date, a cause and an event. "Revolution stuff" carries nothing, and that is the mistake to actually watch for.
Take any sentence from a textbook. Write it in six words or fewer, using at least one arrow. Then cover the book and say the full sentence back from your six words.
Which is the best short note for: “Cells divide by mitosis to replace damaged tissue”?