I find that I get tense neck and shoulder muscles when I do cardio. The other day I noticed that when I get to that point where I just have to grin and bear it through the uncomfortable part, I look up at the ceiling. So I put a sticky note on teh spot I look at that says, "pay attention to what your body is doing!".
The instant reminder of what I am doing subconciously is just the kind of feedback I need to keep myself on track!