Name Writing practice

DHH's penmanship has stalled for a year or so. He can make d and h letters that are enormous, but that's a close to writing as he's come.  Recently I hav felt concern that he's not ready for preschool so I am trying to provide opportunities for writing each day.  I discovered he likes to use sharpie and likes to sit on my lap and write. So we practice that way. Right now he likes to wrote lowercase I.