1. Chill Out
Relax. One of the major reasons you look stiff in photos is due to anxiety and nerves of a stiff appearance in photographs is a stiff bodily pose brought about by anxiety and nerves. Remove your temporary stress by breathing - take a deep inhale in, hold for a few seconds, and exhale slowly. Rinse and repeat 5-10 times (if you're a Pilates, yoga, meditation, or martial arts devotee, you probably have this breathing technique down. Kudos to you).
In one way, your goal is to create the "Duchenne smile", a genuine smile that pushes up your eyes. On the flip side, you're trying to create an eye smile without necessarily being real, so unless you're really good at faking it, follow the remaining steps.
2. Focus On Something
Choose a focus point. It's important that you can center your viewpoint so that your eyes aren't darting about everywhere and creating a sense of being unsettled or uncertain. By selecting a focus point, you have somewhere to aim your look and steady your gaze. People and things to focus on include: the photographer, the camera, the person motivating you behind the photographer, an object at the right height where you've been asked to gaze, or an item of food you really would rather be eating.
If the shot is one where you're able to laugh and smile outwardly, then do so. Think of something funny, even if it involves the photographer's clothing or something amusing that's happened to you in the past. If you can't laugh on the outside, laugh inwardly. What other funny things can you conjure up in your mind that will have your body responding with mirth without a mouth smile resulting? Laughing creates a more natural pose because it relaxes and calms you.
4. Tilt Your Chin Down (Very Slightly)
This causes you to have to glare a little from out under your eyelids, in order to feel like you're looking out properly. And this will help achieve the smize look. Don't overdo the chin tilting. This will lose your neck and have your face looking down, rather than gazing with a smolder at those viewing your photo. Tyra also recommends pulling your shoulders down, feeling your head pulled up by a string, and facing forward.
5. Focus On Your Mouth
At this stage you'll need the guidance of the photographer. Are you smiling openly with the mouth, giving the mere hint of a smile, or looking awfully serious mouth-wise? It gets harder the more you have to keep your mouth closed but that makes getting the smize right all the more important, so that you still portray the smile in your face even when your mouth isn't complying. If you can, practice the smize with your real smile, a very large forced smile, slightly parted jaw, and closed lips. Your jaw should be just open enough for you to stick the tip of your tongue between your teeth. Do this in front of the mirror to see how your face responds each time to the smize and until you find the best look for your photos (unless you're a model, in which case you'll need to get each of the mouth positions perfected). Avoid pouting. Reminiscent of something goats do during mating season, the pout doesn't look that sexy on most people unless they're really adept at getting the angle right pulling a total look together. Pouts are for petulant people in a tantrum mindset; leave it out of your mouth shaping skills.
6. Slightly Squint Your Eyes
Prepare your eyes. The first thing to practice is a little squint that only uses the eye muscles and no other facial muscles. Practice this in front of the mirror until you feel you are able to perform a small eye squint without disturbing the rest of your face. Don't stare; you will notice as you attempt the smize, your temples shift back if you're getting right because you're actually slightly reshaping the expression and shape of your eyes themselves. And the only way to really have that happen is to let the upper facial muscles move ever so slightly as you position the gaze, and then not move again! Just keep practicing – and watch videos of Tyra Banks doing it.
7. Okay - It's Smize Time
Once you've practiced the various parts of the face separately, put it all together and start to actaully smile with your eyes. Once again, use a mirror when you're first learning so that you can see what look you're achieving (or not achieving). Squint just a little (a lot less than your practice in the step before), allow the hunger seep out of your gaze, and focus on the point you've chosen with all the happy longing and smouldering in the world. Seek to exude warmth from your eyes. Without warmth, your eyes will appear soulless and empty. Don't think "cheese" - think "smize".
Try to stay natural in your mindset. While you might be dolled up to the nth degree, you can at least exude that quality of being natural in whatever state the makeup artists have placed you.