I’ve found the easiest two way’s, depending on if you’re alone or have help: to turn the sheet so the elastic is on top holding the outside of the seam, making sure the elastic is loose above the sheet, almost as if you’re ignoring that part, then folding it regularly OR if you turn one corner in and one out so they lay inside of each other and then it creates a nice line along the top and bottom edges, you and someone else would fold opposite sides in (you fold your right hand in, they fold their left hand in) then fold like normal sheet.

I hope that makes sense. Once I learned the first way, I’ve never had an issue with fitted sheets