Is the backspot tossing butt or are they going under the bases' hands to toss? In my experience, tossing the butt led to higher baskets b/c it is easier to use your power from that position, and the flyer is forced to stand up a little bit.
Flyer: make sure she's riding to the top and standing up out of their hands. A lot of the time flyers try to go to a cradle position too early because it's scary to keep going up! So make sure she's vertical for as long as possible and knows not to try to catch and cradle until she's on the way down.
Bases: Well, what I said about the back... and make sure your bases are using their legs. Tell them to use all their power and not be afraid of it! And adding a front spot can make a basket go a lot higher too.