A seated dinner is its own dress code. You will be seen across a table, in low light, for most of the night.
Neckline first
A clean neckline, a good shoulder and one piece of jewellery do more at a table than a dramatic skirt nobody will see.
Fabric that sits
Bias-cut satin and jersey move with you when you sit. Stiff fabrics crease across the lap, and very fitted skirts become uncomfortable by the second course.
Bring a layer
Restaurants and banquet halls are cold. A blazer over the shoulders or a wrap coat on the chair is part of the outfit, not an afterthought.
Dress for the chair you will be sitting in, not the doorway you walk through.