Make sure it's nice & flat to the seatstays, so it doesn't flex at all. Grease the sides of the cam and the block at the back of it.
If at all possible, ditch the arm and adjuster. Use a pozi-stop seatclamp if you can locate one:
Out of the box, I didn't rate them at all, but with good brake blocks and no flexy arm robbing you of stopping-power they're surprisingly good.
Mine's mounted on the chainstays of my StreetBeat, like a 990. The cable's routed through holes I drilled in the frame (sorry, purists).
Works really well.