I heard that using those shaker things you see on TV does indeed help. It looks weird, but I heard from several people who say it indeed works. You just hold the thing in your hand and a shake up and down.
Lifting weights doesn't seem to help. I've tried it myself (I'm male). My doctor says one can't develop muscles to "fill up" the sagging skin. It doesn't work that way, he told me.
Otherwise, try plastic surgery. I had it done to both my arms (last month), and I've noticed a big difference. I still have trouble with stretched out skin, but it's not as bad as it was.
Christopher