Make sure you have a fairly heavy rope that is on the shorter side. Practice consistent singles with your elbows in to your side, only using your wrists to get the rope moving (not forearms).
Watch video up to the 4 minute mark.
Once you have 100-200 consistent singles, it’s time to learn the power jump and how to speed up your wrists for doubles.
Begin with 3 singles and a double and progress to 1 single and 1 double. Watch video beginning at the 4-minute mark.
Make sure you have 50 single/doubles before progressing to consecutive double-unders. Make sure to stay on the ball of the foot and focus on a power jump with elbows in.
Watch the video beginning at the 6-minute mark.