How can I ensure guests continue to mingle throughout a holiday dinner?

One trick I learned is from a book called Entertaining Is Fun from the 1950's, by the famous interior decorator Dorothy Draper. She says to have less chairs than guests. This creates more movement since there will always be people up and moving around.

She also encourages the use of nesting tables and other improvised serving areas, to have drinks on one side of the party, food on the other, and snacks/desserts scattered throughout. I love that book.

I am so tempted to say it -- play musical chairs at the table.

Spacing out appetizers in other areas and bar/drink stations away from the kitchen. The kitchen draws people anyways and spreading it out helps congestion and encourages interaction.

I make sure that I am available to mingle as well...having the apps ready to go, the prep work done, even having dishes that are "make the night before" allows me to host the party as well as cooking. I also have my guests pour wine, and if they ask "What can I do to help?" I let them help...if everyone is helping then they are also chatting and interacting. The best way to ensure that everyone has a good time is to relax and have a good time myself.

I put out Apps on an island in the kitchen. That way while I am cooking guests are in the kitchen with me, enjoying their drinks in food. And it also lets them see everything come together for the meal.