Well, given that we're living in 2014, a woman doctor shouldn't cause us too much difficulty when addressing an envelope.
'Dr. And Mr. Jones' should do it. However, remember that if Jane Jones is a consultant (i.e. A very senior medical doctor), she will not be addressed as Dr. But rather Mrs. Or Ms.
If your primary contact is Mr. Jones, I would suggest switching the names - Mr. And Dr. Jones.
Titles are just one area where getting the etiquette right is important. Here are some other tips for avoiding a faux pas when it comes to business etiquette.
A firm handshake...
...but not too firm. A handshake, historically, is a show that you are unarmed - a friendly force rather than an enemy. That's why you should ensure your handshake is firm enough to convey authority but not so firm you frighten the other person.
Be considerate in your emails
This means not littering your colleagues' and contacts' inboxes with reams of irrelevant, irritating messages. Choose your addressees carefully.
Cut the lift talk
Be discreet. When you've been to a meeting or conference, wait until you're well clear of the building before discussing outcomes and objectives with your colleagues.
