Mine's older now, but over time we did playdough, I have little toys everywhere - squidgy ones, stretchy ones, just stuff to fiddle with anywhere he finds himself (eg in the car). He does piano lessons as much for the hand strength/mobility as to learn piano (which is lucky, because it's tough for him), I have him carry the shopping, he has to try to open his own water bottle/jar before I'll do it for him (we joke that he has one bottle opening per day in him - but actually, he managed 2 recently :D - he's 15).
I make sure he uses his cutlery properly (he uses the wrong hands, but I'm on him about technique).
We were also recommended pencils on rough paper (or even sand paper) and chalk on concrete/walls in order to get the feedback when writing (TBH, he only writes in maths - otherwise he types now).
We tried all the offset pens, weighted bracelets, slanted desks and none of them did it for him - although I know they work for other children
Mainly we're realistic though - that it's always going to be an issue, so sometimes there need to be workarounds - socks a size to big so he can get them on, gadgets to help him grip/open bottles, and not letting him avoid stuff too much, whilst also letting him avoid it a bit because there's no point making life miserable (elasticated trousers, but normal shirts we just leave mostly buttoned up for example)