Unconventional: switch hands for a bit. Most people can write legibly with their non-dominant hand with a bit of practice. After a few days of tears of frustration doing this, take what you've learned about how the pen flows over the page and apply it to your dominant hand. Everything about how a letter is formed is excruciatingly obvious when you are fighting your hand to move in the way you want it, rather than automatically as has been ingrained in your dominant hand.