I started with some principles: writing could go in any direction and glyphs can be written with any orientation or reflection, so they had to be distinct and not differ due to symmetry only.
For alien numerals, each glyph is written in a square bounding region. It touches the sides of the bounds. Each digit (0 through 8) is the simplest curve that has n intersections or endpoints.
I don’t remember what I did for other glyphs. But, one idea is to make the drawing structure based on the underlying sound (or whatever), like Tengwar. In my alien commerce-interchange code, there were a set of A and a set of B and a “syllable” used one of each set. For us we would use consonants and vowels for A and B. Another sound-based species may have different ideas of what sounds to make. A gesture based language for example uses tenticle joints and postures.
So, syllables had glyphs that systematically encode one A and one B value.
A series of posts on the Artifexian YouTube channel goes over some ideas, and he settled on something that was also a “structural” system, not arbitrary glyphs but some architectural correspondence to their sounds.