Nursing is a natural and healthy way to feed your baby. It's also thrilling to realize that, even now, as your body changes in pregnancy, you are already making preparations to lactate and nurse. Your breast/chest tissue is growing, your nipples may change colour and shape of the glands begin to produce early milk for your baby. From about half way through pregnancy, you may notice leaking or crusting of fluid on the tip of your nipple. If you have this (some people do, some don't), you can rub it in as it is an excellent moisturizer to keep your nipples supple in anticipation of your baby's sucking.
You can talk to your care provider about your infant feeding plans to make the decision that is best for you. In the meantime, there is no need to do anything to toughen your nipples or prepare in other ways. Getting some early information and making preparations for support after your birth are the best things you can do to make your nursing experience a satisfying and healthy experience.
Indigenous Midwifery, Breastfeeding – Restoring Traditions, Healing Community
Mayo Clinic - Breast-feeding vs. formula-feeding: What's best?
Public Health Agency of Canada - Ten valuable tips for successful breastfeeding
Canadian Breastfeeding Foundation - Links to breastfeeding resources