art of saying "no"

I had written this post several days back, but I'm posting it now coz I think this is the right time.

Everyone of us are wound up in something sometime somewhere. We cannot just get away from that situation because we want to satisfy everyone around us, and eventually end up doing it for the sake of doing it. So, even in our difficult times, we find ourselves almost incapable of denying. Perhaps, this is where things go wrong. I was reading some blog and this thought suddenly popped up in me. We (especially me) should learn the art of saying "NO" for things that are away from our reach. If you get the "yes man" title in your office, that's it, all work that is potentially incapable for others will be thrown at you, and you cannot get away with it easily, and yeah that's what happening in my case :).
Going out of the way and helping others is good, but not always. Once you get the "yes man" title, I think it is difficult to change back from that. The bitter truth is, people are going to use you if you are like that. 
So new project..learning to say "no" in the nicest way possible. Do go out of your way to help others, but not always. Don't get the title. People tend to use you. It is not their mistake, but it is human nature.