I shape calm / relaxed behavior on a mat or bed, so that they associate relaxing with their mat when I get it out (like when visiting relatives' homes) or when they're told to go to their mat at home.
This book does a really nice job of explaining how to start mat work and the idea(s) behind it. Fired Up, Frantic, & Freaked Out by Laura van Arendonk Baugh
And don't let the title put you off. You're dog doesn't have to be over-the-top to benefit from the mat work method she describes.