Shiva Rea, Beryl Bender Birch, Richard Freeman, and Rodney Yee each offer an asana to help you prepare your body and mind for sitting meditation. You might choose to do just one of these asanas or you might choose to do all four in sequence.
Shiva Rea: Movement Yoga

Photo courtesy of acaciacatalog.com
Spontaneous movement meditation can be used as preparation for any form of meditation practice. Start by standing with your feet hip distance apart, or in a seated posture. Connect to the energy that permeates us by, if sitting, rocking your pelvis slowly forward and back, or, if standing, lifting your arms so that they rise with the inhale and lower with the exhale. As you bring this pulse of movement into your body, allow the current of breath to begin to flow spontaneously in any direction. Simply enjoy how this current of awareness flows and knows exactly where to go to unwind and awaken the kinks and dullness of the body-mind. Complete this meditation by bringing your hands together in a mudra, or sacred hand gesture, to honor the primordial force of creative consciousness within you.
Beryl Bender Birch: Downward Dog

Photo by Laura Berland
Downward facing dog is a posture that I watch my five Siberian huskies do many times a day. It’s a great pose that stretches the legs, lower back, and shoulders, as well as strengthening the shoulders and arms—all of which are essential for happy sitting. I love the posture as it seems to clear the head and sinuses and put everything back into neutral.
From standing, take a deep breath, exhale and fold over, bending your knees and placing your hands on the floor. Walk your feet back a yard or so, depending on how tall you are, to create an upside down V with your body. Place your hands flat on the floor about shoulder width apart, with the fingers spread out. Your feet should be the same distance apart as your hands, balanced between rolling in and rolling out. Spread your toes and press down on the heels, which probably won’t touch the floor. Push your torso back toward your legs. Drop the chin toward the chest, pull in the belly and rib cage. Breathe.
Richard Freeman: Skylark

Photo by Larissa Rojers
The skylark clears and balances the muscular patterns around the spine, allowing us to sit with a grounded base and a buoyancy up the midline. It also opens and balances the breath flow. Begin by folding the left leg back. Be sure the knee joint is comfortable. Sit on a folded blanket or block if necessary. Fold the right leg into half lotus, bringing the right heel as close to the lower left abdominal wall as possible. (Alternatively, the right foot can be placed on the floor inside the left groin.) Reach across the right knee with the left hand far enough to begin tilting the hips to the right. Reach around with the right hand and take the right big toe or place the right hand on the floor behind the sacrum. Gradually push with the straight arm while pulling with the arm wrapped around the back, as if pulling a bow. Breathe. Feel the sitting bones flow down on the inhales.
Stay for about eight breaths, coming out of the pose on an inhale. Then do the other side.
Rodney Yee: Cross-legged Forward Bend

Photo by Adam Brown
Too often our hips are unprepared for meditation and our torso gets dragged down by our legs instead of supported by them. Here is a simple solution.
Sit in cross-legged pose, with your right shin in front of your left. Place your knees right over your feet so that the legs almost form a square. Let your legs be heavy and grounded as your feet are slightly flexed and active. Place your fingertips on the ground behind your hips and press down as you lengthen the sides of your waist. Take all the weight out of your lower back. Slowly bend down, slightly rounding your back and walking your hands forward. Release the tension in your hips, back, and neck. If easy, rest your forehead on your hands. If you are not that flexible, place your head and hands on the seat of a chair. Stay for twenty-five breaths, inhaling in the direction of your hips and exhaling in the direction of the top of your chest. Inhale as you come up, and then change sides, placing your left shin in front of your right, and repeat the process. This posture is great before and after seated meditation.