I have never endured a tear from any of my four births but I was fortunate to be in the care of midwives and I was encouraged to follow my body's cues for labour and birth positions - an essential childbirth right if you are to have the best chance of avoiding damage to the pelvic floor and perineum.
My advice would be to birth on your own terms, in water if possible, but essentially in the position that feels right to you in the moment. This is generally most accessible as a "Childbirth Choice" when you birth with a midwife.
I did a search for you and found a few links of significance. I'm sure other members will be along shortly to share their first hand experiences.
http://www.midwifery.org.uk/thirddeg.htm
A huge list of research articles - take or leave them according to the model of care the women received. An obstetrically managed birth is more likely to result in tearing.
http://www.blackwell-synergy.com/doi....1998.770707.x
http://linkinghub.elsevier.com/retri...20729298002070
(you might need to subscribe to access this article but it asks the very same question you did)
And this compilation of the literature is by our hero Henci Goer:
http://www.efn.org/~djz/birth/obmyth/episabst2.html
There is a lot of jargon to process so feel free to come back and ask for clarification if you can't make sense of these.
All the best,