That said, take a look at those pictures in the "Little Help Here" post. If you have anything resembling a double chin, or even just a wimpy jaw line (I've got a little bit of a double chin, myself), the first thing you want to do is think about stretching the back of your neck really long, and dropping your shoulder blades down into your back. As you do that, your chin will automatically drop down just a little bit. At that angle, your neck looks longer, but you still look like you have a little bit of a double chin, so move your whole head forward - NOT down, but FORWARD, toward the camera. Imagine your chin sitting on a table, and slide it along that table. It also helps if you turn your head slightly to the side: it creates a stronger jawline, visually speaking. If you look at the blue "Little Help Here" picture, you can see how tight the muscles in my neck are, from doing exactly that: This definitely takes some practice before you stop looking like a reject from the psycho ward, but it's TOTALLY worth it
As a contrast, here are a couple of pictures where I forgot to hold my head properly - see the round face?
A pink one:
And a (VERY round) blue one (note the NOT tight neck muscles - I turned my head, but didn't elongate my neck or drop my shoulders):
So hold your head at an angle, drop your chin, stretch the BACK of your neck, drop your shoulder blades and slide your head forward a little. When you feel totally uncomfortable and unnatural, congratulations! That's it! LOL
Now on to full-body shots. The same head rules apply, but now you also have to deal with the rest of your body. :P When someone is taking your picture, stand with your torso directly to the camera, but angle your lower half about 45 degrees and put one foot in front of the other. The angle does two things: one, it visually gives you more of a waist, since you're turning at the waist, and two, the foot-in-front-of-the-other technique (a time-honored Hollywood pose; Renee Zellweger can't NOT do it!) creates a visually slimming line through your hips and thighs. See?
In this first picture, it doesn't totally look like my hips are angled, even though they are. You can kind of tell though, because my shirt is pulling across my chest at an odd angle.
In this (lower) one, I was leaning against a fence, making the pose a little harder to pull off, but it didn't wind up looking COMPLETELY stupid. Although it does look a little uncomfortable. Oops:
Oh, well. What are you gonna do? LOL
So there it is, in a nutshell. Definitely practice before you attend the next big family gathering, though. Otherwise instead of everyone telling you how photogenic you are, they'll all be asking what the hell you were DOING in that picture! LOL