You want to orient the reader quickly so that the realities of a situation are clear. Sometimes the direct approach is best, particularly when there are two characters in a scene. The reader will be looking for clues as to the nature of the relationship and to withhold them can cause confusion. The key is to avoid telling too much all at once, like this:

Jean, a sixty year old veterinarian, and her husband of three years, who is newly retired, sat by the window at Luca's in the heart of downtown Denver waiting for their braised lamb.

Too much information sounds forced. Instead, focus on the most important details. In this case, I'd go with the relationship, but it depends upon the nature of the story. The other details—if they're necessary—can come later:

Jean and her husband sat by the window at Luca's waiting for their braised lamb.

Labels aren't the only way to convey this information. John Cheever's “The Enormous Radio" starts out this way:

Jim and Irene Westcott were the kind of people who seem to strike that satisfactory average of income, endeavor, and respectability that is reached by the statistical reports in college alumni bulletins.

The pairing of the names—Jim and Irene Westcott—lets the reader know this is a married couple. Stacy Richter's short story “The Long Hall" begins like this:

It's so boring where we live that a certain percentage of high schoolers have gone completely berserk—late night partying, stupid driving, sex antics, smoking, and drinking—a lot of kids are doing it, not just Shane and me.

Immediately, the reader knows Shane and the narrator are close and that they're high schoolers. The narrator continues: “But when we first moved here, I thought this was the most beautiful place in the world." That they moved together suggests they're siblings.

Putting the character directly in action can also accomplish some of these important basics. Annie Proulx's “The Mud Below" begins like this:

Rodeo night in a hot little Okie town and Diamond Felts was inside a metal chute a long way from the scratch on Wyoming dire he names as home, sitting on the back of bull 82N, a loose-skinned brindle Brahmacross identified in the program as Little Kisses.

Proulx doesn't need to label him a cowboy. She just puts him on the bull and lets him ride.