When you're in class, emphasize recording over understanding or neatness when you take notes. That doesn't mean you shouldn't try to understand or organize your notes at all; just don't waste time doing something in class that you can figure out or neaten up at home. Consider your in-class notes a "rough draft" of sorts. Rewrite your notes as soon after the class as possible, while the material is fresh in your mind so that you can fill in any gaps completely from memory. The process of rewriting your notes is a more active approach to studying--it engages your mind in a way that just reading the notes doesn't.