Never stop moving. If you stay still for a photo, grown-ups will be disappointed. They love action shots.
Do not look at the camera (at least not at the same time as your sibling or whoever you are being photographed with). Grown-ups like when you assert your independence, particularly when you’re next to a notably compliant child, sibling or otherwise. You want them to remember who’s boss.
Refuse to say “cheese” or smile. Grown-ups like a challenge. They prefer to make stupid faces and gestures in an effort to see you smile. Make ’em work for it- it’s good for their self-worth.
Say “cheese” and smile for one nanosecond so as to appear compliant, yet still avoid having said smile captured by the camera. This is good practice for achieving optimum speed in other areas of life. Remember, as the toddler, you must always be more agile that the adults around you.
Make silly faces. Smile a giant and/or weird smile so that you look nothing like your normal self. Your parents most certainly don’t want you to be recognized in this photo. This is especially true the more people involved and the more anxious all of the grown-ups appear to be. Lots of grown-ups on edge probably means this photo is expensive, and you want them to get their money’s worth.
When in doubt, cry. This is a no-brainer. Crying usually works to get what you want from grown-ups. This is exceedingly true when you are being photographed. Take advantage of this opportunity. Demand candy. Go big or go home.
Bonus: If everyone in the photo seems to be dressed alike, be sure to spill something on yourself at the last minute. You want to stand out. I recommend ketchup, grape juice, or chocolate milk.