The lotus pose in yoga demands hip, knee and even ankle flexibility. To gain that flexibility begin with simple hip stretch. Lie on your back with your knees bend, feet flat on the floor. Place your right ankle on top of your left thigh, just above your left knee. Now raise your left leg off the floor so you get a gentle stretch in the right hip flexor. Clasp your hands around your left shin to help lift the leg. Repeat on the right side. Remember not to over-stretch or go to pain. Although you are striving for "bound lotus" pose, even the most modified lotus pose (such as a simple cross legged position) is acceptable for your practice; after all, it's your practice and yoga is not a competition. Namaste and be well.