Great gaming can happen almost anywhere, just like great sex. But just like sex, it helps to set the mood.
If you have a designated gaming area in your house, put up some gaming-related art. It doesn’t have to be wall-to-wall Conan posters, just a couple of carefully chosen pieces that make you think of gaming. (Having shelves full of gaming books around helps too!)
Even if you play somewhere else, like in a college lounge or at your local gaming store, you can bring things with you to achieve the same effect. Toys are a great option. Playing Star Wars? Put Darth Vader in front of your GMing screen, and set a TIE fighter at the other end of the table. Voila! Instant ambience.
This will help get everyone at the table in the mood to game, and there’s a good chance it will help everyone stay focused, too. (Unless they spend all their time playing with the toys, of course!)