Cursive, or printed lettering?
My cursive was always terrible! Sometimes, just the initial letter, some squiggles and maybe the end, done!
I could read it, but... yeah.
When I switched to lettering, I also was beginning to do a lot of detail work with my hands. Basically took everything I had apart.
You know, "What's inside?"
Most of it went back together.
And I switched to lettering because there was just no fucking way. Cursive and I just do not get along. It is fast, but I just do not flow that way at. All.
That saw an improvement in writing, but the big one was just knocking out essays. Had one high school teacher who wanted one every week. They would pick a rando topic, and GO!
You got about 40 mins to get it said, whatever it was.
He struggled to read them, said I should use pencil, and also said don't cut it short for being neat. He wanted the words, however ugly.
But do patch it up where I can.
So I did. This guy graded them over the weekend and basically wrote back to us. Was a little bit like a message forum. The following Monday we got them back, and all the good stuff was in the margins. Often, he would read excerpts too, for discussion.
This was extremely high value to me personally, BTW.
On some of mine, he would highlight letter combos that sucked. Would suggest challenge words to emphasize them and if I could pack those into the next go, cool! (And points!)
TL;DR: Write every day.
I suggest a journal. Write it, glance at it, patch it up a little and keep going. Get a cool book and a great pencil you just want to write with.
I bet you will improve in a month being able to go back and see where your writing glitches up here and there.
If someone reads it, great. Do what that teacher did. It was fun.
I also suggest lettering, no cursive. If you want, upper case only, making capitals bigger. That is how I started. Kept the problem scope down.
Roughly a decade after polishing it up, I did half a decade of adult tech training where I put notes, problems, you name it on whiteboards. Nobody ever said they could not read it, and yeah, was still upper case, caps bigger.
For techy stuff, you can totally skate on that method. I still use it.
If you can weave detail hand work in, say some craft, or hobby, electronics maybe, it could really help.
I still do scribble a sort of cursive fast for my own consumption. Fast note taking usually. These days I can almost always record or take pictures so that is fading.
But, I gained a little odd skill out of all that, and that is I can usually read most terrible writing! If it has a hint or two in there, mostly right, I am usually good. Can almost always read what doctors write, for example.
Good luck.
Oh and just care a little. Not much, but form the glyphs your way. Have a way. It counts. Adds up.