Dye an Ace roll elastic bandage with Rit Dye to the color(s) that match your camo and then just wrap it around your arm and tuck the tag end under the wraps. It is cheap, easy, available at every drug store and works on any size clothing. I like the stretchy tubes too, like the knee braces that Shawn recommends, but they do not accommodate the same variations of clothing thicknesses and can be a hassle to get off and on. Fred Eichler keeps lots of rubber bands stretched around the hood of his bow quiver to use for keeping clothing out of the way. I prefer the elastic hair bands myself even though they do not tend to stay on a quiver hood as well, but either type of band is a handy solution. The advantage of the Ace bandage and other continuous arm guard devices is that there are not any areas of sleeve material poking out to catch on the string. My favorite is still just a leather arm guard, but there are times when the Ace bandage is a better solution.
Allan