Don't write down everything! It will only give you a hand cramp, and you will be more likely to miss important information. As a rule of thumb, you should be listening about 80% of the time, and writing only 20%. Listen to key words that your teacher says such as, "The main idea is...", "What I want you to get from this is...", and "The important thing to remember is...", which hint what the most important points are. Listen for a pattern in what your teacher is saying, (is he going in chronological order? by cause and effect?) and use these to format your notes. If you find that your notes are messy when you take them, take the time to recopy them and highlight important points later.
Notes from a Textbook:Don't re-write the book! That's just a waste of your time. The whole point of notes are to have a condensed, easier to study guideline, not to have a second copy. Usually for a textbook, it's best to format your notes in an outline, but it depends on the subject. You can use many different techniques such as venn diagrams, time lines; whatever works best for you. Pay special attention to bold and italicized text, and keep a list of vocabulary words.