French seams are a bit time-consuming but a great way of making sure your garment looks as good on the inside as it does on the outside.
- Pin wrong sides together and sew it together at half your seam allowance (I usually have 1cm which leaves me with ½cm).
- Now press the seam (still with wrong sides together). Trim down the seam allowance as close to the seam as you can.
- Open up the two fabric sides and press the allowance towards one side (I find this a good preparation for the next step but I think it can be omitted).
- Press face sides together and pin.
- Sew together at half the total seam allowance.
- Press the seam allowance to the side like in step 3.