I have often been a victim of what Oprah calls "the disease to please" - saying "yes" when I really want to say "no" (and sometimes when I really want to say "Hell, no!"). I do it because I don't want to hurt people's feelings and I don't want to be seen as unfriendly or disagreeable, but I've learned I'm learning how to decline invitations and proposals, how to limit external (and internal) negative influences and how not to agree just for agreement sake. I have learned that saying no to someone else can mean saying yes to myself.
"No, I graciously decline."
Over the last year, I've had to turn down a whole lot of invitations because of pecuniary stressors (i.e. lack of funds). I mean, friends would want to get together and I would sometimes get caught up into what other people wanted moreso than my ability to show up. Now, these are good friends that would offer to pay my way. And I usually accepted, but after a while it really felt lousy being so reliant upon my friends' financial support of my social life. And that was regardless of whether or not I REALLY wanted to hang out - I mean, how can you refuse to show up when it's your friends and when they're paying? Well, I felt more miserable being "on the town" and broke than I did sitting at home.
"No, that's YOUR shit."
The other day, I was at the gym relaxing after my workout. A friend of mine comes over and we playfully gossip - mainly about the people we see. This girl goes into Studio B and does her regular thing - some sort of dance routine that reminds me of moves I see in music videos. Later, 5 really young girls (about 19-24 years old) appear and join her - apparently they're working on those moves together. My friend notices them and says "Oh, look, they've brought their lunchboxes!" and I say "They must be video hos-in-training!" My friend repeats that to another guy working out nearby and, bemused, he says "God bless every one of them." And I felt stupid and cowardly, because I didn't have the courage to do what he did. He basically said, "No, that's YOUR shit and I'm not getting caught up in that." I want to be able to do the same thing. Gossip is a pervasive and insidious negative influence; I don't need that or any other destructive energy in my life.
"No, I don't agree with you."
I've been in so many conversations where it's so easy to just agree, nod my head and move on. The purpose for me to be in any conversation, though, is to understand and to be understood. Whether I agree or disagree. If I disagree AND it's especially important that I'm understood, the onus is on me to explain why I disagree. But lots of times, it's not even that deep. It's possible for me to disagree and not feel any obligation to explain any further.
I can always say "No."
It was difficult at first, but now I have a tendency to say "no" whenever I'm not absolutely certain that I want to do anything - and I'm the person that defines the criteria for my decisions. I can conserve the effort I expend in agreeing for those precious moments when, yes, I agree and when we connect. That is not going to happen each and every time, and that's okay.

I think I’m guilty of the same disease … Seems as if I’m always trying to please even when I know it’s not healthy for my health. I’ll bend over backwards to please whomever … I’ll have to put “No” into play and go from there without feeling guilty because I did so.
You and me both baby, you and me both! :-(
(But a change is gonna come)