The first dance, it is one of those shots, along with the register signing the first kiss and the cake cutting. A cornerstone shot - one we all do. This is my recipe ... Two speed-lights on stands either side of the dance floor, angled in a little and normally around 1/8th power. The set up gives you a variety of shots. Shoot into the light and you can get a nice silhouette effect - and you know how much I like a silhouette. Shoot from the other side and you get a beautiful cross lit couple with the crowd nicely illuminated in the background. You can of course add a bit of on camera fill for even more variations on a theme.
This is a recent shot from Helen and Jon's wedding at the fabulous Old Kent Barn. On this example I even managed a bit of lens flare from my old 24mm prime.