There's English Paper Piecing - make hexagons the finished size out of freezer paper and iron them to the wrong side of the fabric hexagons. Iron edges over the freezer paper and hand-sew. I had trouble with this using 1/2" hexagons. I ended up just using the hexagons as a guide for where to sew.
So, that leaves another option - use the freezer paper as a guide as to where to sew. Or use a plastic template to mark the sewing line on the wrong side of the fabric.
The most important part is to start and stop sewing 1/4" from the edges of the hexagon. And to stay on the sewing line.