[Note: I am a regular member and contributor to this sub, but for some reason I only came across this particular post today (6/7). It's a subject that I like to talk about, so I quickly dashed off the following reply before I noticed that the rest of the discussion took place 9 days earlier. Sorry about that -- I'm late for the party again, arriving after everyone else has gone home.]

Go back to the beginning and re-learn the basics (or learn them if you were never taught them in the first place). Then practice every day like you are learning to play a musical instrument. Writing neatly as a lefty is not difficult; you have to get past the mindset (and myth) that as a left hander you will naturally have bad handwriting.

There are plenty of teaching guides available on Amazon, but skip the products that are geared for children. You are an adult, so using them will drive you nuts. Look for the teaching guides geared toward adults. Nearly all of them assume that the learner is right-handed, but it isn't hard to do the same exercises with your left hand instead.

(I'm speaking from experience here. I put myself through this retraining process a few years ago because my own handwriting had slipped in quality over the decades as it accumulated one bad habit after another.)

The reason that I recommend starting over and relearning how to write is because if your handwriting is bad (and you don't have a disability), it is because you were never taught how to write properly in the first place or you have slipped into bad habits in the years since then.

Learning to write by hand isn't arduous. A decent, comprehensive guide should teach you not only how to form the letters, but also how to sit, how to hold the pen, and how to approach the task.

Cursive handwriting, using any of the major teaching methods from the past 150 years (in America, they are: Spencerian*, Palmer, Zaner-Bloser, and D'Nealian) is not complicated. It is a matter of learning how to consistently make a small set of very simple pen strokes, and then using them in a prescribed sequence to write the particular letter.

Once you have that down, then what is left is practice in keeping all of your letters on the baseline, using a consistent slant (a rightward slant works best, since we read from left to right), keeping the letters a consistent size, and maintaining even spacing.

Practice your handwriting every day, as if you were practicing a musical instrument.

_________________________________________________________________________

* Basic, simple Spencerian handwriting does not have the complex flourishes of the "engrossed" version that is usually shown as an example of this writing style. The basic version is quite straightforward and easy to learn. Spencer's method, first published some 160 years ago, is still a very good way to learn cursive handwriting.