Get a grocery bag and load it up with some groceries from your pantry. You can also use a bag of books, a briefcase, a suitcase, etc. Place the bag on your left side. Bend down to pick it up. While carrying the bag with your left hand, maintain your best upright posture. Don’t let your shoulders creep up to your ears. Relax your jaw. Walk around the house/office/etc. Then do it with your right hand carrying the bag as well.