A lot of people, women especially, ask me how to strengthen their arms...specifically the area behind their arms that jiggles, wiggles, wobbles...whatever term the use to describe this unwanted motion that's happening.
First, there's not one exercise out there that's going to magically shrink one area of your body. Full body strengthening plus cardio plus clean nutrition will! However, I can tell you that good ol' push ups can be your best friend when it comes to upper body strength.
Here's a great way to do them so that you're working through full range of motion...
Hand Release Push Ups: get in position for a pull up (on knees or toes) with hands under your shoulders and your spine neutral which means your eyes are looking a bit forward, not straight down and definitely not behind you. Lower yourself all the way to the ground then release your hands at the bottom for just a second. Put your hands back down on the ground and push all the way back to your starting position.
These are harder than traditional push ups but you'll like the benefit you'll get when it comes to getting rid of that wobble, jiggle...or whatever you call it! :)