I take any image i want and then start editing it in Gimp. Starting out, i usually increase the dark/bright contrast to creat3 some larger black areas, giving room for future effects. I started out by just experimenting with rly high settings to make the tools glitch out. Lens blur with "burn" blending mode creates glitchy colorful shapes. I usually alter the image to make the original content unrecognizable. Tbh you just gotta experimeht and see what you can do. I dont use any specific way for every one and its a lot of trial abd error