Learn good technique and then don't overdo it. I think I've done it the wrong way in every way that's possible and I've paid the price. I'm not saying that I do it all right now, but I have learned a little and I've learned to not strain as hard as I can--keep it moderate and just cruise. Keep the sprints to a minimum.
I know that high angle is supposed to be the right thing, but I've lowered my angle and lowered the pain. I try very hard to maintain the paddlers rectangle and let the torso do the work, but I'm not fanatcal about it.