Be educated. Be educated about common things that happen in labor and delivery, today. Know the risks of common medications given in labor. Birth is BIG business. Its very expensive, but easy to care for. The maternity ward is the big bank for the hospital, so don't be surprised that you aren't informed of the reasonable risks of choices you may be offered. Look into all of your birth options, as well. Water births, home births, hospital births, birthing centers...most women dont' even know they HAVE this many options today! Consider a midwife, as well, rather than an obstetrician. A certified nurse midwife is a great alternative to an OB if you are reasonably low-risk. They deliver at home and in hospitals and can even offer epidurals, narcotics, and pitocin if necessary during labor. I am a fan of natural labors, whenever physiologically possible, because no narcotics going to baby is better than even some. But...I'm an even bigger fan of control and education. Whatever your choice, make sure its your own. There are different kinds of unhappiness with a birth. There is a general dissatisfaction, "Man, I wish it could have been easier." And then there's anger and resentment that really take hold of moms after a birth. The anger and resentment comes from lack of control. And lack of control due to "God" is also different than lack of control due to physician desire and nurse incompetence.
I recommend watching the Business of Being Born, by Ricki Lake. Great documentary.
Labor itself? Have at least one person there who shares your desires for your birth. Do not count on being able to defend your wishes when it becomes necessary.
Physiologically, do not fight the contractions. Concetrate on breathing rhythmically and relaxing your pelvic floor muscles completely (don't do kegals during a contraction!). I also recommend hypnobirthing and Bradley methods.