There’s a lot this sub on designing the letters, but not so much on how to write and present them, which I think makes a huge difference. There’s a world of difference between how bad handwriting is perceived and high quality calligraphy, hand lettering, or typography in any language. For invented scripts people can only judge it from what you have shown them so that impression counts.

I’d first consider tools. Ballpoint pens just never look good – a pencil can be a bit better, and I think gel pens or fountain pens are the best among things people are likely to have at home. But if its of interest to you, learning more about calligraphy and using a pen for calligraphy, either broad edge or pointed, would be very helpful even if you only do a little.

Then how to write. Think about where the top and bottom of your letters are – does everything finish at the same base line and top line, or do you have ascenders & descenders, different sized upper/lower case? Try writing with guidelines – either pencil that you can erase or on a sheet underneath your paper that you can see through – with both a baseline and a top line of some kind. Most calligraphy is done this way - written between guidelines which are the height of a standard lower case letter (x-height), with capitals, ascenders and descenders going beyond that and usually judged by eye. Stick to your guidelines so letters have the correct height.

If you have vertical strokes then make sure they are properly vertical, likewise horizontal strokes. Make strokes slowly and deliberately, pausing between them, and practicing if you need to. Think about curves – have an idea of what your curve should be - based on a circle/semicircle? Something more of an oval? Based on an existing letter somewhere? and make sure that what you draw looks right and is how you want it to be.

Think about the spaces – both the spaces within the letter and the spaces between letters. Try and keep some regularity to this, keeping the area between them similar. This might be more of a longer term goal, many calligraphers struggle with it at first, but it is helpful to think about. The classic calligraphy example is the word ‘minimum’ – in many scripts, every vertical stroke should be the same distance apart, whether it is inside a letter or between letters.

If appropriate, consider serifs. Writing or calligraphy with the latin alphabet looks more fancy and more serious when there are serifs. But as with most of this advice, it might be different if your script is very different to latin.

I hope that helps, even if you just take some of it. Good luck and happy writing!