STOOP- lean over and, if you're a smaller cup size, gently tug the bottom of the cups down and jiggle to make sure your breasts sit completely in the cups. Make sure the apex of your breast is lined up with the center of the cup.
But, for larger cup sizes, skip the jiggle and do this:
SCOOP- while leaning over, use your opposite hand to put all your breast tissue into the bra cup. Scoop your breast from under your arm and under your breast and into the cup. Make sure the apex of your breast is in the center of the cup.
And finally, for everyone while standing straight:
SMOOTH- with your pointing fingers inside your cups at the center, smooth your breast tissue along the top inside edges of the bra cups.