When You're Ready to Think About Seating Arrangements …
If you have decided to have a buffet, everyone pretty much expects to fill their plates and find their own place to sit. The only time you really need to worry about everyone sitting at a table is at a barbecue, a formal meal, or when the bride is opening the presents.
Here's how to plan the seating: If you have the shower outdoors, you can rent nifty garden furniture, take any sturdy metal-legged stuff out of your house and put it in the yard, and let people sit on benches, lawn chairs, or whatever. If you are doing it on the grass, DON'T take out any wooden-legged furniture, and test the ground first to make sure it's hard enough to hold someone sitting on it. Some little chair legs will sink right into the dirt and topple your guest!
You can make benches from two really large planters (with something in them, like a big plant!) and two 2” × 4” pieces of lumber. You can rent lawn chairs or make this the perfect occasion to justify buying that patio furniture you have your eye on.
If you are doing it inside, you can also bring in lawn chairs, especially if they aren't too ratty-looking. Usually, the bride sits in the best chair in the house, and it's decorated specially for her. Everyone else is arranged in a sort of horseshoe shape, especially for gift opening.
Set up seating so people can sit in groups of two or more, preferably with little tables to put their stuff on nearby.
Creating the Seat of Honor
Your bride is the guest of honor at your shower, even if the mayor's there. She should have a special chair with optimal views of all the other guests, especially during the gift-opening part of the shower.
One of your wingback chairs will work just fine, as would a captain's chair from your dining room. Decorate it in advance with balloons and lay a streamer across the seat that says “Reserved for Betsy.” You could drape it in velvet, plump it up with extra cushions, or spray paint an old chair gold and glue tiny fake jewels from the hobby store to it. You could tie wedding things to its back, like the traditional decorations on the back of the bride and groom's getaway car.

