also an even load of washing i.e. if you have a full load, dont put all the heavy stuff (jeans, etc.) at the bottom, spread it out.
Secondly, I had a machine that was under a counter and it used to move slightly and touch the sides, my solution was to put a sponge, a cheap thing from the pound shop will do, on either side of the machine, and these acted as a buffer between the machine and the side wall of the press.