Short answer, I just say no to bigger lips.  Many patients forget what they originally looked like before entering the world of injectable fillers.  I tend to be very conservative with injecting lips and often show patients their original photographs before repeating injections.  I almost always avoid injecting the entire length of the lip, sparing the lip area at the corner of the mouth.  This can maintain a natural transition of the upper and lower lip and not create a "fish lip" appearance.