I tore on hands and knees too ... one first degree tear, one second degree tear. I only pushed for 21 minutes, and dd was "normal" sized -- 7 lb 10 oz, and I don't remember her head circumference offhand, but it wasn't anything outrageous. My guess is it was due to the really short pushing time, which didn't allow the tissues to stretch. They also told me to stop pushing when dd's head was halfway out so they could start suctioning her

:, but that's a whole different complaint. I'm sure it didn't help matters any with the tearing, though, having her head sit like that for a period of time.
I had been in hard labor for 36 hours and was desperate for the birth to be over, so I was pushing with all my might. I also never got an urge to push, so I was pushing without any guidance from my body. I think if I hadn't been so exhausted, and had been able to wait for my body to be ready to push and pushed more in that kind of rhythm, things probably would have gone better.
Anyway, I'm doing a homebirth this time, and I actually feel intuitively that I'm going to tear again. I think this is because they stitched the 2nd degree tear, and it has just never felt "right." I don't have any pain, it just feels different in a way that I can't explain. Every time I think about this upcoming birth, I feel that I will tear again, but only enough to allow my body to heal on its own so that the area will come together properly again.
I don't know if this helps any

, but I think a slower/longer pushing phase might help things. I also know that a position like a squat tends to shorten the pushing phase, so you might want to avoid that. But really, I would push in whatever position feels intuitively "right" to you.