This seems to be one of those things that tend to scare a lot of people – but really aren’t hard at all and today I’m going to show you how to sew french seams!
I PROMISE!
Personally, I don’t think they are the solution to every seam (there are so many options!), but they are a beautifully neat way to finish raw edges and are particularly well suited to sheer and lightweight fabrics. Also, they are a nice option for those who don’t have sergers/overlockers and want a nice professional finish. Once you try them you’ll honestly find tonnes of situations in which they are incredibly useful.
Here’s how to sew a lovely french seam:

I’ve used a fabric with a digital print, so it’s easier to see which is the right side and which is the wrong side.
Instead of placing your fabric pieces with the right sides together, place them with the wrong sides together (ie right sides facing outwards)
Make sure the side seam edges are lined up correctly.
Sew 3/8″ from the raw edge.
*Please note that other measurements for french seams may be used, but this is the way I do them – mostly a personal preference so that I don’t have to change seam allowances on patterns – ie your total seam allowance will still be the standard 5/8″ after using my method*

Then grade (trim) the seam allowance back to a scant 1/8″.
Open your seam out and press the seam flat.

Now fold along the seamline so that the right sides of the fabric are now facing each other, and the raw edges of the seam are enclosed.
Sew 1/4″ from the folded edge, encasing the raw edges and finishing your seam.

Press your seams flat, and admire your pretty, pretty french seams!