I cheated and read the other suggestions first, so I'll just try to add to theirs.
Before delivery, run around the house braless as much as you can. Wear a shirt loose enough that it will shift about as you move. If your breasts have already grown and you need support, you could cut the nipple area out of an old bra. The friction from the shirt can help to "toughen" up the nipple area so that it's not so sensitive once nursing.
I nursed all 5 of my children. When my milk came in, my breasts were HUGE and SORE (first time I went from a C to a DD cup). Nursing frequently can increase the milk supply, so isn't always recommended. A warm shower or wash cloth can help the milk to flow and release some of the pressure. (I would sometimes stand in the bathroom with a warm washcloth and hold a clean bottle to the nipple to catch the run-off - frequently would get about 2 ounces without even pumping.)
The hospital often gave me some sort of ointment to put on my nipples after nursing. I found the best thing to do when at home is to let each nipple air dry after baby has nursed that side. Once completely dry, coat generously with plain old petroleum jelly (Vaseline). This helps to keep them mosturized and to not crack. When using the vaseline at home, I would also use an old, soft washcloth as a "nursing pad". You can even put some vaseline on it. Of course, you wouldn't want to grease up when going out, but a very light coating would absorb and not get on your good clothes.
Make sure that your diet remains healthy AND that you are drinking lots of extra fluids. Remember to try to not eat those foods that make you gassy, as that can pass through your milk also.
Relax, Relax, Relax -- especially when you sit down to nurse. But try not to get too stressed about anything, as baby will sense it. And old wives tales claim that if the mother is stressed, she will pass that through her milk, and baby gets colic. Not fun.
Once last thing to remember, is that when the milk flow first starts (each time you nurse), it triggers a release of hormones through your body. These hormones can cause cramps, as they help to shrink your uterus back to its original size. Also as the milk releases from the milk ducts to flow to the nipple, you often feel pain. If you can just make it through the first few weeks, it really does get much better.
As a new mom, I would switch back and forth from breast to formula. With each successive child, I nursed more and bottled less. My last one was exclusively breast-fed, and actually would refuse to take a bottle. I enjoyed breast feeding because in our busy world, breast feeding "forces" you to sit down and just relax and enjoy your baby.