It is too ugly to write with a pen holding posture, mainly because the pen holding posture is wrong. Pencil, pen and brush have their own correct pen holding posture. As long as you master the correct pen-holding posture, your handwriting will look half good. At the same time, sit upright and don't sit sideways, which is also helpful for writing.
Learning the structure of Chinese characters is ugly, also because I don't know the structure of Chinese characters, which parts should be big and which parts should be long. If you don't know it in your heart, it's wrong to write it, and the words are not good-looking. If you want to write well, first learn the structure of Chinese characters, understand the structural proportion of each part, and then write, the words will look much better.
Practice more brush strokes, and the strength of each stroke is different. Writing brush calligraphy is the most basic way to practice calligraphy. Only by practicing brush calligraphy can you easily write other words.
Read more famous copybooks and learn some basic writing methods. I think it's ok, but others still don't look good. Find some famous copybooks, see how others write, find your own gaps, practice more, and make rapid progress.