How can I make sure my nipples don’t point to the ground? (Photos)

From your provided photo it appears your nipples are currently in a good position. When the implants are placed they will settle naturally behind the nipple. It is unlikely that the nipples would turn down. That is more of a risk for those who need a lift but decide not to have one.

Your nipple to fold distance should be on maximum stretch to estimate the largest implant you should go with. At 7 cm, an implant around 200 cc is optimal; at 7.5 cm, 250 cc; at 8 cm 300. Keep in mind that this is generalizing, and your tissue elasticity can change this equation.