Obviously the more people in the group, the more difficult it may be to coordinate so I recommend choosing a color theme like "blue and white", "pastels", "fall colors", etc. and have family members choose clothes along those guidelines. Remember to COORDINATE but you don't have to MATCH.
Think about the weather. Yes it's Florida, but we have changes in the seasons too. During December, January, and February, it can get chilly. You may laugh when you're up north and I tell you it's "cold" here (and you're sitting in a snow storm) but you'll realize what I mean when you're shivering on the beach with a cold northern breeze blowing. On the other hand, June through September are HOT and HUMID with a chance of evening showers on any given day. The ocean breeze makes it humid and wet-so quick dry clothes for men are a plus and short dresses and skirts for women look great and make it more comfortable.
Once you've narrowed down your outfit, put it on and look at yourself from the front, side and back. I will capture every angle of you at some point during our session so consider if you're happy with how you look from the side and back as well. Is it worth it to wear shapewear for an hour to smooth out any lumps? Does your bra strap show? Does it need to be ironed? It's best to realize these things before walking out the door.
Think about the details. Jewelry is great, but a necklace that we're always worried about making sure is hanging right can become a distraction. I'm not intentionally focusing on photographing your hands (unless it's a wedding or engagement photo) but old, chipped nail polish is never a good look for photographs.
SHOES-a beach shoot will probably start with some photos on a street or park so bring something photo worthy. When we get to the beach I always recommend everyone do the same thing-either everyone takes them off-or everyone leaves them on. That way it looks intentional. 99% of families choose to go barefoot, because it's a beach shoot after all!
The wind is probably going to blow on the beach. I do the best I can to work with the wind but if you have long hair that is going to constantly blow in your face and ruin your photo, please consider an updo or bringing along a headband or hairclip to control it.