"Do not automate buggy software."
I was thinking about the failed automation projects I’ve been involved in during the last few years and I seem to find a pattern. All those projects were very, very buggy. I realize now that you should only aim to automate functionality which is fairly stable, so that you do not expect to see a test failure in more than about 1 of 10 test runs. If you see that your tests are failing 50% of the time, then automation is not the cure for your problems. Try to find out why this is happening in the first place.