Should I be tensing my abs when jumping rope? I tried searching a bit online and couldn't find anything saying one way or the other, just saying that jumping rope worked out your abs.
It's not a technique I've used or heard of before. If you start raising your knees when jumping rope you'll get an additional ab workout anyway, so with my own advice would be to stay relaxed and just work the rhythm.
I haven't heard of it being actively taught. Like Simon said: raising your knees higher will add work to the hip flexors and abs. Double unders I feel them more in the core, but I never actively tense that region.
I found I got good at skipping by starting with my jumps really high to give the rope more time to pass under me. Then over time jump slightly less and less. Then try jumping from one foot to the other. Eventually you just find yourself skipping.
It's impossible to jump without engaging your core. Just try bouncing on the balls of your feet and feel what's happening. It's not something you have to think about, it just happens.
