Writing notes is really important, especially later in life so it's important to start now. You might think that you will remember everything but you really won't that is why we write it down. Write what you think you will need in the future. So really think if you will need it later or if you don't need it and it's just unnecessary. Sometimes teachers repeat stuff, so don't re-write anything unless the teacher tells you to do so. Don't write down everything your teacher says. Not every sentence or word is important to write down. Also, even if you think you will remember what your teacher says, you should still write it down. This way when you come back to your notes, you will reread your notes over and over again.

 Writing notes is really important but what size should your handwriting be? This part depends on the person. If you have trouble reading, maybe write a bit bigger. If you can't stand "wasting space" in your notebook, write small. But don't start writing small just because people say you write big. You should be able to read and understand your handwriting, if you can't you may have to write bigger or smaller. You may even have to change the font. Just remember these notes are supposed to be for you so you should be able to read the notes easily. 

People use a lot of different things to write like a pencil, pen, or even a highlighter or colored pencil.  But pen is probably the best for looks but use a pencil if you are solving a problem for math so that way you can erase it. Stay away from colored pens and highlighter. Only use a highlighter for important stuff but don't actually write with it, just use it to highlight. This is because highlighters can be hard to read especially if the color is yellow, and color pencils are more meant for art so why waste these colors when you can just use a pencil or a pen? It also depends on what the teacher wants you to write with, too! However, in general, pencils are the best way to go, especially mechanical pencils!