I've not been published (yet), but I have worked with over 50 photographers. Here's some tips for "looking your best" which I've learned over the past 2 and a half years:

1. Choose a photographer like you would a babysitter! Feeling comfortable with the person is the MOST important determinant of how the pictures will come out. I've worked with very talented photographers, but felt uncomfortable, and few of the pictures turned out "good" or even "acceptable". Talk on the phone with the photographer. The ones I've felt most comfortable with were those who I easily talked more than 10 minutes with before meeting. (I intend on writing more on how to choose a photographer... but for now you can look at my other guide for some safety tips).
2. Call and cancel the shoot the night before if you get into a fight with your significant other. Call and cancel in the morning if you stay out too late. I'm not encouraging you to cancel, but such things can make you look tired and not at your best.
   
3. Avoid the following foods (if possible) within about 24 hours of your shoot: popcorn, whole wheat (and other high fiber foods), anything with alot of salt (so most processed foods), Americanized chinese food (ethnic cusine is healthier), and other "heavy" foods. I usually stick with pretty high-protein foods the day or night before so I'm not feeling so bloated. If you're a woman, try to schedule things right after "that time of month". This will make you LOOK your thinnest and also feel pretty good.
4. Know what makeup colors look best on you. This might sound obvious but, double check that your foundation color matches your skin. I've accidentally worn orange-ish foundation because the make-up counter girl said it was "my color" -- use YOUR judgment- and even look at yourself in different kinds of lighting. Neutral colors around the eyes look great in almost any photo (actually can't think of where browns look BAD).
   
5. Put mascara on a bit heavier than usual. Especially if you want to bring out your eyes, cake it on in midnight black! Eyeliner also helps. I've never regretted wearing "too much" mascara in any photo. Powder under your eyes will prevent "raccoon eyes" as the day wears on.
6. Light "nude" lipstick never looked bad with lipgloss. Sometimes, depending on the lighting, darker red tones can look orangish or gothic. I like tinted gloss. You should bring along a few shades of red, if you're into the brighter colors.
   
7. If you're a guy, you might want to consider tinted face moisturizer or powder to even out your skin tone, especially if you're getting headshots done. Moisturized lips also are preferable to chapped or dry lips.
   
8. Assuming that you're shooting in a studio: bring alot of clothes! Depending on what looks you're going for and how many outfit changes you have planned... you will always want what you DON'T want! Bring extra pantyhose and stockings. Also bring along your face powder, lipstick, and lipgloss. If you're a guy, bring several colors of shirts. Don't shy away from bright clothes.
   
9. Ladies: bring your sexiest HIGH heels! This is a great time to wear those heels you can barely hobble in. It's worth it during the shoot. Not only do heels make you LOOK sexy by emphasizing the curve of the back, hips, bust, etc... but they make you look about 10lbs lighter and (ofcourse) taller. When they make you feel really uncomfortable, take them off (so you don't look uncomfortable), but even in waist-up shots, heels can make a difference in posture.
10. Speaking of posture... hold your shoulders back and suck it in! Even if it's from the elbows up, you can still often tell the difference.
    
11. Hopefully the photographer will guide you into some poses and moments. Assuming that you've chosen someone experienced, they should guide you into poses which make you look great. The photographer should NEVER touch you, unless maybe your hair (and even then, he should ASK before). Most photographers know this, but it's amazing how many don't.
1. Assuming that you're maybe on a budget and going with someone who isn't the most experienced photographer or are having a friend take your pictures, look at pinup art before the shoot. Those OLD pinups (Vargas and the like) were poses meant for "real" women with curves! Bring a book to the shoot, if you're afraid you might forget. Most of those poses will help a woman look attractive, no matter what size she is or what clothing she is wearing. Ofcourse, if you're just going for some business shots, then forget the previous and just suck it in and make sure the photographer gets a variety of angles while you look all professional.
   
12. HAVE FUN! If you're having fun, feel relaxed, and comfortable... as I said at the beginning, it will show.