Jessie E Turner
      Tatted Lace
Making the Basic Double Stitch
The dark thread circles the left hand.  Light thread to the shuttle. Lift the light thread out of the way.
Shuttle goes under the dark thread until the thread drops over the back end of the shuttle.
Back the shuttle out.  Light thread will slide off the right fingers as you continue to pull the shuttle to the right.
Curl the middle finger of the left hand into the palm. Pull the shuttle sharply to the right until the shuttle thread is taut.
Keep the tension on the shuttle thread.  Lift the middle finger of the left hand to pull the dark thread into place
SECOND HALF OF THE DOUBLE STITCH
FIRST HALF OF THE DOUBLE STITCH
Let the shuttle thread hang down.  Go over the dark thread letting the thumb slide between the thumb and the shuttle.
When the thread clears the end of the shuttle, back the shuttle out.  The thread will slide between the finger and the shuttle.
Hold the tension on the shuttle thread while you lift the middle finger of the left hand and pull the stitch into place.
Click on image below to enlarge picture.
Use variegated thread. Coats Aunt Lydia's size 10 
Red, White, Blue works well.
Here are two double stitches correctly made. The shuttle thread slides through the center of the stitches.
Here is a knot in the first half of the next double stitch. The loop is on the shuttle thread instead of the ring thread
This is a knot in the second half. Again, the shuttle thread cannot slide through the stitches.
Diagrams of stitches and knots.
To correct a knot, increase the size of the loop (knot) on the shuttle thread.  Release the tension on the ring thread. That means curling your middle finger of your left hand into your palm so that the ring thread is slack. Snap the shuttle thread taut by pulling the shuttle sharply to the right. Keeping the tension on the shuttle thread, lift 
your finger to coax the stitch into place.