I am a big natural childbirth advocate and feel the best way to achieve a natural birth, is to be prepared mentally, physically and emotionally for the journey ahead. I think first time moms need to prepare the most since they have little to go off of, but "experienced" moms should prepare as well because every birth is different.
The mental part is the most powerful and influential aspect of birth. If you are confident and informed, you will feel prepared and positive about labor. If you are fearful and clueless, you will look at birth as something you will suffer through.
There are many ways to prepare yourself mentally, these are a few of my suggestions:
Take a child preparation class, here are some options available:
Read a book, these are my favorite:
Ina May's Guide to Childbirth
Gentle Birth Choices
The Birth Book
Thinking Woman's Guide to a Better Birth
Husband Coached Childbirth
Childbirth Without Fear
Join a few Facebook pages, they have great articles and birth stories:
Loving Labor Doula (mine)
Preparing yourself physically is extremely important. Childbirth will be one of the hardest things you will ever go through, and you will need to have stamina and power. If you are already exercising, great... keep going :) If you aren't, these are some awesome low impact ways to keep fit and prepare your body.
Having emotional support during labor is key to having a successful natural birth. I high suggest that you choose wisely who you are bringing into your birth room, and prepare them as well.
The Birth Partner is an awesome book for anyone that will be present during your labor and delivery.
Investing in a doula is a great way to help insure a natural birth. Statistics show that having a doula present at your birth will lower your chances of intervention and use of medication, and help produce a greater satisfaction of your labor and delivery.