The correct way to down shift while braking involves a technique called "heel and toe" used by race car drivers. In order to not shorten the life of the clutch by using it as a brake pad, place the ball of the foot on the right edge of the brake pedal and roll the right edge of the foot onto the throttle briefly to bring the engine rpms up while the clutch is in. The idea is to match engine rpms with transmission rpms in the new lower gear instead of relying on clutch friction to do it for you. Your down shifts will feel smooth and will sound like a formula 1 car braking for that hairpin turn at the end of the straight; "vroom, vroom, vroom". You can impress all your friends. You can also take the stick out of gear without using the clutch, so if executed perfectly, use of the clutch is entirely optional. Screw it up though and you'll grind the gears.