If there was one thing we have to name we struggled with for the longest of time, it would be rope jumps. Yes, you read it right; the movement any 4-year old could do with ease. Rope jumps.
Anyway, a true athlete will train the weakest part the most, and so we did. Singles. Singles. Dreaming of singles. Even doing singles in the office. Other people in the office starting to do singles. And finally, we got it, realizing we were only half-way. Double-unders. Ooookidoki.
Now, there are a lot of theories around on how you should do 'em, lots of youtube videos, tutorials, websites, articles....
First, make sure you have your singles perfected. Meaning you can do them unbroken for a long period of time and that you are able to pace yourself easily, being able to alternate between slower and faster jumps.
Second, practice jumping up a little higher in between. For example, jump regular for 3 jumps, then jump a little higher for 1 jump. Not high like this or this, but just a bit, ok?
Hand positioning is key, and Chris Spealler explains here where you should keep them.
Now, here's is the point where it gets tricky. We had the problem Chris describes, tensing up and and letting the arms go wide. If this happens, go back to singles and focus on keep you arms in place and keeping a relaxed jump.
do-able, but the mind-body connection didn't quite work that way.
Finally, we figured a different word-use just worked better. Whip the rope. Now don't go running around whipping everyone, but simply tell your wrists to whip it.
Ok, it's starting to get weird now, but you get the point.
When using a proper speed rope, this might do the trick for you like it did for us. Good luck!
Get your speed rope at Rogue, WODRope, JumpNRope or RPM Rope to name a few.
P.S. Here's a tune to help you on your way ;-)