You may want to experiment with pencils and grippers. Ticonderoga pencils did wonders for our boys.

They are thicker pencils that you just sharpen the old-fashioned way. The claw worked for one of our sons and not the other. Clicky pencils didn't work
at all at first, but now they can use them and both prefer them. So, just trying out some things and asking which your ds prefers would be good to do. Plus, he can have some say-so in it then.
I think less writing done better is the goal at first, and you can tell ds that.

So, alternating you writing with him writing is fine to do. He can write a sentence, and then dictate one for you to write, and you can switch back and forth. This will rest those fine motor muscles in between. Likewise, alternating writing assignments with non-writing assignments is important. Spreading the writing out throughout the day helped both of our dc become better at it. So ds doesn't also have to focus on how to spell things, writing his answers on a markerboard for him to copy on paper helps. This also gives him a model to look at as he writes. As far as cursive, here's a past post about that, that may help to know how to approach this with your ds:
viewtopic.php?f=6&t=7762&p=56647
Legibility is really the #1 thing to teach when it comes to handwriting. No one has perfect handwriting, and everyone's style is different. But being able to read it is a must. So, IMHO, that is the goal I'd work toward with your ds. Many, many dc (and many, many adults - with many, many of them being men

) do not have "neat" handwriting, but if it's legible, it works.

Ideas are more important than perfect writing, so it's good to really encourage a child's ideas, especially a child whose writing is not so great, as they may feel there's no point in sharing their ideas in written form otherwise. HTH!
In Christ,
Julie