In my opinion, choosing the right kind of pen is very important. I use ballpoint pens mostly and prefer some pens much more because of their tip, weight , thickness and shape.

I have really bad handwriting. All my teachers used to complain about it back in school. I did improve it slightly over the years with practice. But nowadays I type on touchscreen or keyboards 95% of the time and in the rare occasions I use a pen I have starting trouble and my handwriting gets really really bad. Hell ai cant even write stuff on a straight line. Writing may become less frequent in the future in most jobs I guess.

But that being said, if you wanna improve it keep practicing, hold the pen properly and choose a pen with the type of tip that works best for you. You can even practice on those handwriting books.