ive procrastinated on asks for so long im so sorry. i personally dont follow any specific guidelines for making my borders if that makes sense? i usually draw a square or grab one off somewhere and doodle around it (most professional resource maker ever) ^^; the biggest issue is getting it to repeat properly, but i personally just do trial and error until i get it right. i recommend keeping the size to 100x100 or 200x200 if more detailed & adding stuff mostly to the corners rather than the sides themselves, but it all depends on what youre going for !!