The answers given are all good ones, but I have one more to offer. You can, after cleaning the inside of the hopper, rub the surface thoroughly with powdered graphite.....or actual gunpowder.
I actually condition my new powder measures by rubbing over the inside surfaces with a bit of gunpowder. I generally use a flake or ball type powder, rather than a stick powder (for reasons that probably seem obvious). Bullseye works great for this, for example.
Works very well. I started doing this after getting a new powder measure one time, then realizing that I had no dryer sheets on hand. So, I used what happened to be at hand - and it worked perfectly.