i sew them like i would anything else pressing the seams open and matching , making sure i have that 1/4 inch if its black line to black line, i have pined the line like i was sewing a line instead of up and down pins using them sideways if that makes sense to you. sometimes i have to go back and rip a short area out some have suggested basting the lines
then sew i think i had the best luck with my sideways pinning.