French Seams are a great option for sheer or lightweight fabrics or if you don't have an overlocker and require a professional finish. The downside of using French seams is that it does take more time that a regular seam as there's a couple of extra steps.

Here's how to sew French seams: 

1. Place the fabric WRONG SIDES together and pin.

3. Press the seam allowance to one side and then trim the seam allowance a few mm from the stitching line.

4. Place fabric RIGHT sides together, encasing the trimmed seam allowance. Make sure you fold the fabric along the previous stitching line. You can press the seam along this stitching line to get a crisp finish. Pin.

6. Press the seam to one side so that everything lays flat. 

7.  Optional: Top stitch seam allowance down. This will stop the seam allowance from moving around, but bear in mind that the top stitching will also be seen on the right side of the garment.