Take Your Time - Don't sit down to this job the night before the wedding - it may take a while! Getting everyone in the right spot will really make for a more enjoyable reception for everyone.
Categorize - If you're keeping a master guest list, categorize each guest by one of the following: bridal party, groom's family, bride's family, coupled friends, single friends, guests with children, and people with known standing conflicts.
Make a Plan - Now's the time to put your artistic side to work! Get out a sheet of paper and plan out how the tables will be arranged including the bridal or head table. If you will be dictating where each table will be placed put yourself where everyone can see you, leave enough space for dancing, and take into account foot traffic.
Start With You - Your first feat is to decide who'll be joining you and your new spouse at the head table. Some include the entire bridal party, others sit with their parents, other couples sit alone. It's your call and will, of course, depend on your venue as well. If your bridal party is sitting separately, consider placing them all at one or two tables and include their significant others as well.
Family First - Next up: the family. Usually family members get dibs on the tables closest to yours. Use your best judgment and place people with their own family making sure to separate anyone who might not get along. We want everyone to play nice at your wedding.
Create Cliques - It's best to keep your friends together with their friends-work friends at one table, college friends at another and so on. If, say, your tables seat 8 and you've got 9 work friends attending your wedding, you have two choices: either add another chair and squeeze everyone in or put four at one table and five at another. Whatever you do, don't put the ninth friend at the table with your book club. That would be awkward.
Singles Only - The moment you've been waiting for! Who needs a date? If you've got enough single friends to form a singles table - go for it! It might be fun to see if your wedding is the start of another lifelong relationship. It may be nice to ask your single friends if they want to be included in your little experiment.
The Kiddie Table - Depending on your venue, it can be nice to place your friends who have children together. They understand each other. They can commiserate and wrangle each other's children together. They can sprawl all of their baby and kid gear up and down the table without worry.
Ultimately, though, this is your call-you know your crowd better than anyone else. Will grouping kids together make parents feel isolated or a sense of solidarity?