With your face toward the mat, put your hands on the mat and rest on your elbows. Curl your toes under. Using your core strength (abdominals), make your body stiff and straight like a plank.
Breathe. Hold this position. Start with 30 seconds, and work up to one minute. Tell jokes while holding the position. And keep breathing.
Challenge: Instead of resting on your elbows, put your hands on the mat under your shoulders and do the pose with straight arms, like the top of a push-up.
Further challenge: Do some push-ups. Keep breathing.