French knots are necessary in embroidery. They are the only knots small enough for fine detail. A lot of people dread having to make a French knot, but they really aren't that bad. They come in very handy for making single dots. For example, polka dots or rain drops.
You will start by bringing your thread to the front of the needle. Make sure you hold the thread securely with your left index finger and thumb. Make sure the thread is away from the fabric.
Making sure the needle is pointed away from the fabric, wrap the thread over and around the needle with your left hand. If you wrap twice you will have a smaller knot. If you wrap three times you will have a larger one. It depends on your preference.
Try to hold the thread tightly drawn with your left hand. Turning the needle in a downward position, start to take it in reverse a few threads away. Do not use the same hole. Doing this may make the knot pull back through and disappear. Making sure the tip of the needle is inside the hole, slide the knot down the needle onto the fabric. You will need to pull the thread snug with your left hand at the same moment. This is where the tension can come in. Try not to tug the knot too hard. The eye of the needle will not fit through the knot as the thread goes to the back. If it is too loose your knot will be sloppy and it won't lay flat.
You will have to calmly jolt the needle through the posterior part of the material while clenching the knot in place beneath your thumb. Holding the thread down with your thumb can help you to see the knot. Begin by pulling the thread through. Continue to pull until the thread disappears under you thumb and it is completely pulled through. Congratulations on your first French knot!
It will feel awkward at first. The secret is to remember to hold that left thread taut. Whether you use your fingers or thumb depends on what feels better for you. This stitch would be much easier if someone shows you in person. You will need to do this stitch many times before it comes naturally. I have been doing these knots for years and sometimes even I run into problems. So don't get discouraged. Remember that practice makes perfect. You will be a pro in no time!