Well I think for us.. it was the one month I didnt think we'd get pregnant, because dh was going away in the 'O' time.. but one thing we did different was we dtd every morning before dh would go to work and I'd go back to sleep with a few pillows under my bum..
Before that we were doing it at night or arvo every day for a few months and nothing happened.
Also, stress less and dont think about it. But I am one not to follow that rule, because it is darn right impossible to forget something that you want soooo badly!