Hi Hope,OK most wifes just love being sucked, tweaked or just massarged, gentle, some the can get an orgasm form it, but just be gentle, and if you wifes not to big and your good you can sometimes get the nipple to the back of your throat, they love that, but just be gentle as some day it may be feeding your baby. trust me then you will get jealous.
Good Luck
Ive never seen problem with it or heard of it being problem