The most important things you want to do before the birth of your baby is to learn as much as you can about breastfeeding. One of the best books on breastfeeding is called "The Womanly Art of Breastfeeding" and is published by La Leche League, an organization soley devoted to helping mothers breastfeed their babies. Attending a La Leche League meeting if they are available in your area is a wonderful way to ask questions that you have. You can even just call a La Leche League Leader. They are always more than happy to answer your questions. Go online to find information on the La Leche League website, including local groups.
A preparation you may want to make is to find nursing bras and clothes. They are not essentials but are very useful. You should buy them at the end of your pregnancy when you can try them on for the best fit. I would also recommend buying one size larger as well. Leave it in the package in case you don't need the larger size but after the milk comes in you may need an even larger size. Motherwear.com has clothes that allow for discreet nursing in public.
The most important thing to remember at birth is to put the baby to the breast as soon as you can. Giving baby a chance for the first nursing during the first two hours after birth increases your chances for a good start. Make sure your nurses and doctor know that you want to nurse your baby right away. They can lay baby on your chest skin to skin and dry baby off right there. With a blanket over the top you can give baby all the warmth he or she needs. Another very important factor is to avoid any artificial nipples. Bottles or pacifiers require a different suck and may cause baby to latch on improperly at the breast. Finally remember to put baby to the breast often. Baby needs to nurse 10-12 times in 24 hours, that is about every 2-3 hours. The more you nurse the more milk you will have. Frequent stimulation of the breast stimulates milk production. The first 2-5 days there will be only very little of a yellowish substance, called collostrum. Collostrum is very important for the baby. It has many anti-bodies and disease-fighting substances. After those days the collostrum will slowly change to milk. Keep nursing often to prevent a build up of milk. It takes about 6 weeks for the demand and supply between baby and you to come into a good balance.
These are the most important things to know to have a successful start to your breastfeeding relationship. There are many more things to know after you get started. So please seek out that information. Congratulations on choosing the best for your baby!