I do sort of what QuiltE does, except I'm lazier.
I stab a pin through the seams I'm trying to line up, then I dab a tiny dot of washable school glue in the seam allowance and press it dry. Then I take the pin out and I'm ready to sew.
If you press your seams open, just run a stiletto between the fabrics to un-glue them, then press.