This a is a really wide field. Basically its starts with one of the standard algorithms, like and l-system, a voronoi diagram, or simple combination of sin and cos to draw shapes. Have a look at thi-ng[1], just as example for a library that has implemented a lot of this kind of algorithms. The next step in my process is to think about how to destroy this forms as most of them are used a lot in this field and become boring. Using perlin noise as input to arguments of the algorithms is one way to do this. The other part is to make most all of the input variables easily changeable as most of the time the whole process is like writing the program and then spend a lot of time adapt the parameters until you get some interesting output. So in the end I have a small Svelte app, using Svelte only cause the data binding for the inputs so simple, which has tons of sliders that renders an SVG that can be saved in the end.

[1]https://github.com/thi-ng/umbrella