Well, here's how to use body language to make sure they pay attention. These tips come from clinical psychologist James Houran:

• First, make your suggestions count. For example, when it's time to choose vacation destinations   set your chairs at a 90 degree angle--So, one of you is facing North, and the other is West. The direction doesn't matter, it could be South and East, it's the angle that counts. Why? Men feel face-to-face interactions are aggressive. But this way he isn't forced to make eye contact, so it short-circuits his stress response, and lowers his defenses. The result-- He'll be more receptive to your suggestions.
• Then, make your statements memorable. For instance, to help your forgetful dad remember to pick up his prescription, when you talk, stand exactly one foot away, with your body facing his. What does that do? By violating the accepted personal distance between adults   which is normally one-and-a-half to 4 feet   your words will seem unusually important--And he'll remember what you said.
• And the final way to use body language to make people listen is--Literally, get them on your side. For example, if you want your stubborn teen to do the impossible   like, clean their room - try this. Face in the same direction, and stand beside them so your shoulders are just a few inches apart--Then, simply turn your head to make eye contact. Side-by-side means nobody is in a position of authority, and that you respect each other. Bottom line: adolescents are more likely to do what you ask when they feel respected and independent.

If you'd like to go further, check out the book: Reading People by jury consultant, Jo-Ellen Dimitrius