1. Neutrals are your friend. You don't want your clothes to take away from the subjects of the picture (that's you and your family!). Steer clear of bright colors and large logos.
2. Patterns can be beautiful in pictures when used the right way. For example, if dad is wearing a plaid shirt, take the colors from that shirt and dress the family in the colors found in the pattern. That way the pattern does not look too busy, and the rest of the family is dressed in complimentary colors.
3. Consider how you plan to use the pictures. If your holiday pictures are for your Christmas card only then using seasonal accessories (like Santa hats and Christmas trees) are fine. If you want to frame the holiday pictures in your house year round, then you may want to avoid those accessories.
4. Instead of matching, choose colors that compliment each other. For fall photos I like hunter green, navy, maroon, mustard yellow, or burnt orange for accent colors. Pick two or three of those colors and use grey, ivory, beige, and/or denim to tone down the 'busyness' of the colors.
5. I love dresses or skirts for mom. They add intrigue and variation into a picture. And it looks great against a nature background!
Pro Tip: Professional pictures are awkward. There's no avoiding it. Trying to act natural in front of a stranger (photographer) while a camera is pointed at you can be, well, weird. The best thing to do is to interact with your family while your photographer snaps pictures. Tickle your kids, smile at each other/your kids, throw them in the air, kiss each other/kids, spin them around, hug, etc. This will produce the most natural looking pictures. Who knows? You might actually have fun taking your holiday pictures this year.