1. When you want to say no: "Thanks but I'll pass." Too often, people beat around the bush to their detriment as well as the recipient's.
2. When you want to suggest something, instead of just suggesting it, which could engender defensiveness, try what I call California Couching: "Your point is interesting. I'm wondering if it might be a good idea to (insert your idea.) What do you think?"
3. When you want to say yes but appear strong: "That sounds good to me." Not, "Fantastic!"
4. When you don't have all the information you need to respond intelligently, don't try to BS your way through, say something like, "Tell me more." or "I'd like to reflect on this. I'll get back to your tomorrow."