The pull technique is what I used to use in garment sewing many years ago. But you don't pull on opposite corners unless the fabric is square to begin with. If it's not square, find the spot on one side that would make a square, and pull that spot, which will be the true bias, with the opposite corner. Move both hands down about six inches and pull on that square. Keep going until you get to the other corner, then keep going on that last triangle, right into the final corner. Then go back and do the first triangle, too.
If you start a few inches from the first corner, you might understand it better. Just keep pulling on the true bias.