Suggest spinning rear wheel and applying brake afew times before adjusting;this may centre the shoes a bit.To adjust the brake, firstly loosen the outer cable adjustment lock nut, wind the adjuster into the threaded bracket so that the adjuster goes right into the bracket as far as it will go,then put a mole grip on the cable hard up by the actuating lever so that the cable cannot slip looser when the cable clamp is loosened, pull the cable tighter with the mole grip, tighten the clamp , spin the wheel listening for rubbing sounds, adjust the cable until you need a only a small brake handle movement to lock the spinning wheel, and yet no rubbing noise is heard with the wheel spinning and if left to spin it doesn't suddenly stop from only spinning slowly(ie it slows down to a stop progessively).