I observed in my son's class that a fair number of kids reversed letters up until second grade. A certain amount of that can be normal.
Practice, practice, practice! We bought Handwriting Without Tears and did a page a day for 6 months, both volumes. My son never had any issues with reversing letters or holding the pencil, but his penmanship got better with practice.
Have you thought of trying piano lessons? Again, practicing fine motor skills can be helpful.