French seams are used on fine and sheer fabrics, and they give a more attractive finish than simply overlocking. However they can be a bit fiddly and many sewers give up on them, but here is a way to get perfect seams even with the wigglyest of fabrics!
Here my total seam allowance is 10mm, so I stitch 3mm, and then 5mm from the edge. The extra 2mm is taken up in the turn of the fabric.
Begin by stitching the wrong sides together at 3mm, this is half a foot width on my machine: