The BEST bit of advice I ever received before giving birth was an almost throw away comment about 'The Ring of Fire'.
It didn't make much sense at the time, as I was expecting my first baby. And the comment was something along the lines of:
If you feel the Ring of Fire, don't push. Just breathe through it.
When my time came, I was blissed out in the bath, my body was pushing. Then I thought to myself "it is burning". BURNING! FIRE! RING OF FIRE! BREEEEEEEATHEEEEE.
I actively prevented the pushing, and justed breathed. The burning passed. And on we went, a baby born on the next contraction. AWESOME. No tearing.
The burning, or stinging, felt at this point is the body's way of saying 'slow down, I am not quite stretched enough'. By panting or breathing through the burning contraction, you give your body more stretching time. Your body adjusts to make room, and you can move on.
Working with your body, not against it.
So to avoid tearing here is a bit of sage advice:
If you feel the 'ring of fire', a burning like sensation, don't push. Pant, breathe, slow down.
When it passes, with the next contraction, push.
Only bear down on contractions that don't 'burn'.
Of course, sometimes, our bodies just do it, and we can't control it so much.
I have seen some awesome warrior birthers, who do tend to tear, because they push through.
I have seen others do the breathing down, and not tear.
Interestingly, it doesn't seem to take longer. A bit like weaving through traffic. If you rush, you really only use more fuel and wear (and tear) on your car, if you relax and take your time you save fuel and energy, arrive more relaxed. Often both cars arrive at the destination very close together.
It also helps to birth upright (on knees for example), rather than on your back.