MSNBC and Prevention Magazine summarize simple principles of persuasion and negotiation, and they further discuss examples for putting them into practice.
Kalee Thompson writes (excerpt):
1. Speak confidently
Get directly to the point, but make sure you aren’t domineering. . . .
2. Make eye contact
Holding someone’s gaze calms them, according to studies, and indicates you have something serious to communicate. . . .
3. Be expressive
Smile, gesture as you talk, and nod while others speak to show your interest. . . .