I try to use some of the dimensions within the quilt , to give an overall continuity to the final look. If have been working with a log cabin for example an the cut width has been 1.5 inches , I will make the first border at that cut width,,, then working out to another diminesion within the block. If the block contains 2 , inch 3 inch or 4 inch etc.. cut dimiensions.. those are the ones I try to work with ... and occasionally after a few narrow will use a finished block width for a additional border that has some detail of the block to tie the design back to the body of the quilt.