Generally I dig a front facing, full torso shot with Arms, Jewelery, hair and other people and things out of the way so the boobs are unobscured.
If clothed, the lower the neckline the better, if naked, the sharper the angle away from center, the more difficult expanding the existing brests without shape and nipple placement getting proportionally distorted. Also clothing should be as solid medium shade color as possible, as this helps reshading for depth.
Lighting is very important, shadows thrown by the head arms or other objects make the expansion trickier.
cleavage and skin tone should be clear and sharp because stretching blurs, so the better the source image, the more room you have to expand before it becomes obvious. If your model is naked or in a bikini, sometimes you can cheat by stealing some thigh to stretch over a very bloated breast to even give back some original skin texture.
The same technique can work if you have a petterned dress, stealing a bit of the torso can be wrapped around the bodice so the stretched boobs don't betray the expansion by showing stretched patterns.
pop quiz tomorrow.
