I used to have really bad chicken-scratch printing and I wanted to improve.
The exercise that really stuck out for me was to find a font I liked in a book on calligraphy and started practicing the alphabet.
Before I started practicing, I didn't pay much attention to how I was forming a letter, I'd just draw it - and it would look messy. Once you start looking at each letter as a discrete number of strokes you start paying attention to the small parts and the whole looks much better.
If you're really lucky, you'll find a guide with arrows showing which way to draw each stroke. Super helpful. Note that this font uses a fountain pen, so it'll look different with a standard ballpoint: