taking a walk and just flinging it sidearm (so i dont have to use a lot of power to get a good snap) and having it skip/skid across the (preferably semi-smooth) pavement. If it's premium plastic, i put a circular weight ontop of the disc, which is resting on concrete (the smoother, the better) and hold 2 opposite sides of the rim and without pushing down, move it in a circular motion. This is to make sure I get even wear, every 5 seconds worth of rubbing, i try the disc out and throw it, if it needs more breaking in I'll titrate. I also usually try to aim to wear it in enough so that it's almost where I want, then i take the disc and use 1000 grit sandpaper (wetsanding) and smooth the ground-down area. This usually works well for me.