I was thinking, "If there was one bit of advice that would stand me in good stead for my SEO efforts, what would it be?" This inspired me to try a little experimental poll. I realise I myself am not adding any content of merit here (I just don't have the experience to do so), but I think that the answers of the community here will more than compensate. That being said:

1) If there is one bit of advice you would give about SEO right now, what would that be?

2) If there is one bit of SEO advice you wish you'd been given (say, in the last couple of years), what would that be?

3) If there is one thing you wish your clients understood or did not ask of you, what is it?