Is this a new problem? Are you sure he's "lazy" or is it a real struggle? I ask because handwriting was extremely difficult for him as a child. I didn't develop "nice" writing until after high school. My father had the same issue as a child and and my newly 11-year-old still struggles greatly. It's dysgraphia and DS gets accommodation for it (he still has to hand write but he also is allowed to type most things.)
I can recommend "Handwriting Without Tears." It's a great program and the reason my DS can write anything at all to be honest.