Moisturize moisturize moisturize
This goes for both sexes. Whether your bottle is a $250 luxury cream or a cheapie Walgreens purchase, use it. For optimum results you should be moisturizing daily, but at least attempt to make it a regular step in your day for a week before you picture appointment.
Yes, sleep well...but don't oversleep. Get a solid 8-ish hours of shut-eye for several nights before, and resisting the temptation to sleep in on a weekend morn means less chance of puffy eyes.
Make a water bottle your best friend
While you're taking care of your face with all that moisturizer, keep up maintenance on the rest of your body by drinking more than the recommended eight glasses of water a day. A healthy, happy body often means a healthier, happier appearance. No binge drinking for the few nights beforehand, and especially not on super-sugary beverages like massive margaritas from chain restaurants.
Wear a shirt of a darker color
Fingers crossed that your photo ends up being overexposed versus under. A lighter image irons out skin wrinkles and lifts a year or two off your age. To make your face appear brighter and younger, search your closet for a dark, solid color top that works well with your skin tone or eye color. For example, we wore a royal blue sweater to bring out our eyes. Navy blue is always a good bet.
Apply minimal, natural makeup (ladies)
Passport photos are used to identify a traveler when they're at their very worst; this means the moment they show up at immigration after suffering a long flight with dry air and fatty food. If you're not planning on wearing a full face of evening makeup at 6am at London-Heathrow after a flight, then don't wear it for a passport photo. The less time an immigration officer spends squinting at your photo, the better.
Trim facial hair and sideburns (men)
The woodsman look can be pretty hot, but it only makes the airport officer's job harder. The look you should be going for is of a person who is responsible, sane and worthy of entry to whatever country at which you've just landed. Immigration wants to see the contours of your face, not your impressive 1800s US president-style muttonchops.
As much as we loathe using a Tyra Banks word, it completely fits the sort of smile appropriate for a passport photo. No frowning, and no cheesy grins. A simple upturn of the corners of your mouth or "smizing" (smiling with your eyes) is perfect. Think a happy thought and it may even happen naturally.
And, whatever you do, don't try to imitate this 5-month-old's first passport photo: