It's good practice to offer vertical art experiences for children--ie: at an easel or with paper taped on a wall, fridge, fence, etc. Working vertically strengthens different muscles in the shoulders, arms and wrists that helps build fine motor control necessary for writing. Also, when children write vertically their hands and wrists are naturally in the correct position for writing. Therefore, if they practice this position a lot, muscle memory will help this become their regular position.
We have a large easel (from IKEA around $14) downstairs and a tabletop easel upstairs in the studio. We've also put a big sheet of paper up on the fence to paint, and I have a little magnetic dry erase board on the fridge that Q likes to write on.
For younger children not yet writing, offer magnets on the fridge or washer/dryer. As they manipulate and move these magnets, they are using the same wrist and arm muscles as writing.
