Messy writing.. How do I fix it?

Practice, practice, practice! Just like they made you do in school when you were a youngin. I think most of us learn to write, legibly or not, when we're little and it's difficult to suddenly change something we've been doing for years and years. It's a part of you now. The only thing you can do is practice and try to slow down when you can. My brother, who is 40, still writes like a child.