Practice is important to getting the timing necessary to successfully link several consecutive Double Unders. In my opinion, It's best to be able to link approximately 50-100 consecutive single skips before trying to master Double Unders. If CrossFit has tought you anything, foundation is critical to success and mastering form at the principal level is the correct approach.
It's common when learning to do Double Unders that the rope will whip you leaving temporary marks. Where you are getting whipped can be an indication on how to adjust your timing... getting into a rhythm is critical to the success. Both wrists should be working in unison, often if one wrist is ahead of the other the rope will slightly bind and you end up getting whipped.
CrossFit HQ has a few good videos featuring Buddy Lee, Worlds Leading Jump Rope Training Expert.
http://media.crossfit.com/cf-video/CrossFit_PittBuddyLeePosture.wmv
If you are looking to purchase a quality speed jump rope, Amazon.com has 2 decent ropes at a respectable price.
10 ft. Speed Rope by Valeo ~ $5
The best rope I have found and the only one I use is an
Ultra Speed Cable Jump Rope $13.95 at www.buyjumpropes.net
