Here is a brief tutorial on making french seams. This is a beautiful finish on semi-sheer, light weight fabrics. Most seams can be finished using this technique. Set-in sleeve armseye seams will need to be bound with a bias strip of fabric, as a sharp curve is not easily done with a french seam.
Start by stitching an accurate 3/8" seam, with wrong sides of the fabric together.
Next, trim the seam allowance in half, leaving about 1/8-3/16".
Iron the seam flat first, to meld the stitches into the fabric.
Now iron the seam to one side. I like to do this from the wrong side, to avoid leaving a little crease next to the the actual stitching line.
Iron the seam with right sides together, and the stitching line exactly following the fold line.
Sew the the next row of stitching at 1/4". The original 3/8" line of stitching, plus this 1/4" now equal the full 5/8" seam allowance.
The finished seam held up to the light to show the inside structure.
Press the seam to one side and you're done!