Kickbacks are a great way to work the triceps and, if you've been lifting weights for any length of time, there's a good chance you've done a zillion or so.
If you want to spice things up while adding more muscle groups to the mix, this core kickback is one way to go. The idea is to hold a plank position while doing your kickbacks which, you'll notice, is very challenging. Not only do you have to keep the hips down and square while holding your body up with one hand, you have to do it while extending a weight behind you again and again. Not an easy task (and not for beginners, of course).
The key is to take the feet a little wider for more support and to position your supporting arm more towards the middle of your body. It's also key to use a lighter weight here, at least at first, to practice your form before going too heavy. If you need a modification, put one knee down on the floor if you start to lose your form.
Do it right: Get into a plank position, on the hands and toes, feet wide. Hold a light weight in one hand and pull the elbow up next to the ribcage. Make sure your hips are square to the floor and your body is supported. Holding this position, straighten the arm, sending the weight back and squeezing the triceps. Lower and repeat for 1-3 sets of 8-16 reps on each side.