Hair
If you're getting a hair cut for your shoot, do so about two weeks beforehand. For men, a fresh cut a couple of days before the shoot is fine. Come hair-ready and bring a brush, comb, etc. in case you need one.
Hair accessories
If you're shooting outdoors, be ready to put your hair up and make it look nice in case of a windy day. Bring bobby pins, hair clips, headbands or any other favourite accessories.
Glasses
If people wouldn't recognize you without glasses, you want to wear glasses in your shoot - however, the glare on glasses can detract from your eyes in photos. You can have your lenses removed from your frames for your shoot or you can also visit an inexpensive company online and buy a suitable pair of duplicate frames.
Red eyes
Visine will help reducing redness.
Lips
You will probably wipe or lick your lips during your shoot, so bring fresh lip gloss or lipstick to do touch-up. Use lip balm for a few days in advance of your shoot to make your smoochers look their best.
Teeth
If you want to brighten your smile, start your treatments about two weeks before your shoot.
Breakouts
Start using African Black Bar Soap/or your usual product for a week in advance of your shoot to help reduce and limit pimples and blemishes. Equally important, don't cake on a lot of make-up to try to hide blemishes - it's almost always easier to Photoshop away pimples than to clean up overdone make-up.
Make-up
Do not use Retin A and Alpha Hydroxy creams (causes skin peeling that will show with photo makeup). A subtle application of make-up can really soften your skin and accent your facial features. But make sure it matches your skin tone, or your face may look orange compared to the rest of your body. Make sure you use professional help or use tips online how to do a photo shoot ready make-up. Don't forget to finish with "NO SHINE" setting powder. Bring the powder with you to touch up if you need it. For men: Shine-Control Blotting Sheets work well.
Facial hair
Men, be freshly shaved with a new razor, shaving cream and a moisturizing after-shave lotion to avoid bumps and redness. Trim up your beard, sideburns, mustache or goatee, especially looking for wiry stray hairs. Ladies, even if you have some light facial hair (particularly around your lip or chin), indulge in a waxing in advance of your shoot - even barely-there light facial hair will be noticeable in your photos. Men and women both, pluck and clean up those eyebrows.
Moisturizer
Dry skin can really detract from a great photo shoot. Start moisturizing nightly a week in advance of your shoot. When you get out of the shower, dry off until lightly damp, and slather on moisturizer. Focus on your arms, shoulders, neck, face, hands, anywhere you'll be exposed to the camera. This includes your legs if you're shooting in shorts or a skirt. Pro Tip: For dry skin on your face, especially around your nose, use a sugar scrub. Mix a cup of sugar with about a quarter cup of olive oil, or just until it looks like wet sand. Scrub your face with it anywhere you have flaky skin, wash it off, then wash with soap to remove the oil.
Nails
A fresh coat of nail polish will make a world of difference in your photo shoot. Pick a neutral color that won't distract in your shoot or clash with your outfits. Freshen the morning of the shoot, then be careful not to scuff it while prepping.
Bloating
Ladies, avoid high salt and high fat foods for two to three days in advance of your shoot. Being bloated will sap your confidence and comfort in front of the camera.
Undergarments
Bra straps won't do anything to help your outfit look its best. Be sure you bring a set of bras and strap-adjusting accessories to work with any outfit you want to shoot in to keep those straps well-hidden.
Sun burns/Tan lines
If you plan to tan before your shoot, do so at least a week beforehand. Be mindful of clothing tan lines, sunglass tan lines, hat tan lines, etc.
Ironing
If you iron, iron the night before and then hang the clothes for your shoot. If you're wearing something that wrinkles easily, don't wear it in the car on the way to the shoot - just change at the location.
Shoes
Ladies, can't go wrong in heels or wedges. Men, clean'em up!
Eat!
Be sure to eat something before you leave for your session so you're not hungry during the shoot. I can't stress this enough. You will look better, be more focused, and have the energy throughout the shoot. This is especially important for children. A great idea would be to bring crackers, nutrition bars, etc; but stay away from chocolate or colored items/drinks, etc. Three days before your photo shoot, avoid to eat red meat and spicy foods (these items can give you oily skin and swelling).
Dad
Have a fresh shave or trim, and use a new razor with shaving cream and a moisturizing after-shave lotion to limit bumps and redness. Make sure nails are clean and trimmed. Wash your hands. Clean up your shoes. Moisturize and scrub away flaky facial skin. When you wash your face, pay attention to eye boogers and sleep crusties. For wardrobe, go for jeans / pants, tucked polo / dress shirt with a belt, or go casual with just a T-shirt / un-tucked polo, button-up short sleeve, etc. Again you don't have to perfectly match the rest of the family, just wear something that coordinates.
Mom
Women know what to wear, but in general, unless you are extremely thin you may want to wear something that covers your upper-arms. Long- or 3/4-sleeve tops are very flattering. If you wear jewelry, aim for subtlety, and be aware of it twisting or turning.
Kids
Same advice as above, but again, everything needn't match, simply coordinate with the parents' outfits. If Dad's in a T-shirt, don't put the kids in dress shirts.
Practicing facial expressions and poses with you family in front of the mirror will definitely give you more confidence and better results. Bring a smile!