I like to have enough fabric to cut a bias strip from selvedge to selvedge. To get a true 45 degree bias cut you will need 45" of fabric. I then fold the fabric from upper left to lower right making a large triangle.
Cut along the fold. Put one piece aside. You can then fold again in half lining up the cut edge folding from bottom to top.
It is then easier to cut with it folded. This way I get the greater number of long bias pieces. When sewing together for a large quilt I will alternate the shorter pieces with the longer pieces.
Binding Note: Make sure you lay the bias binding on the edge of your quilt to make sure a seam does not fall at the corner. If this does, then shift the binding forward or back to avoid this. If you cannot avoid it then cut the binding and re sew so the seam does not fall at a corner.