We all know how important it is to use our asana practice to tap into the core, the literal and symbolic center of our power. But instead of focusing on the rectus abdominus (the "six-pack"), the focus should be on working the deeper layers of the abdominal area, such as the transversus abdominus. Switching from the six-pack to the deeper layers takes subtle awareness, so be patient even if you can't access the muscles right away. (When all else fails, try laughing, since you use the transversus to laugh or cough.)
Or try this simple exercise: Lie on the ground with your knees bent and your feet flat on the ground. Bring your fingers to your lower belly to feel your TA engage. Lift your legs off the floor, with your knees over your hips and your shins parallel to the floor. Breathe normally as you slowly tap your right toes to the ground and return to neutral. (The slower and more controlled your movements, the more you'll work the TA.) Do the same with the left foot. Repeat 4 times, feeling the strength and power contained in your mid-section.