here's the method i've found for maximizing curls/volume and minimizing frizz:
flip hair upside down and put hair from front middle section (closest to forehead in the bowl of the diffuser, and hold bowl all the way against scalp so it is "scrunching" your curls for you. THEN i turn the dryer on, pressing the cool shot whenever it gets too hot for my scalp. i then TURN IT OFF before removing the bowl from my scalp. then i go to the front right section and repeat, then front left, then flip right side up and get the underside, then flip back upside down and get anywhere i missed. i don't diffuse until 100% dry, and it doesn't look quite right until it's finished airdrying all the way and i flip upside down and scrunch again.
the key is only having the blowdryer on when the bowl is against your scalp because this minimizes your hair getting blown around and thus minimizes frizz.