1. Get rid of the outer cable stop arm thing. Use a cable hanger, maybe an Odyssey "pozy stop" seat clamp that has a hanger built in (or just go to any bike shop and get a seat clamp hanger and bodge it onto a seat clamp)
2. Now you are rid of the hanger arm, the body of the brake will sit flush to the frame. Use cable ties to hold it hard to the frame. If the cable ties are too thick then you might need to file out a small channel in the ally body for the tie to sit in.
Those are a few of the things I always used to do and they helped no end. BUT, they are still a bit crap.