Do your pull ups palms facing away from the body (like you are holding your handlebars).
Face down, body held rigid in plank position, lower chest to floor and raise up. If you need to, start out building push-up strength on your knees and work up to toes.
Kneel on all fours with one end of an elastic exercise-band (swim cords work great here) tied to your right ankle and the other end to an attachment point beyond your feet. Extend your left arm and right leg out and then crunch them in bringing your right elbow towards your left knee. Round your back, exhale and pull your belly button hard up to your spine as you crunch in, hold for two seconds and repeat.
Lie on your back with your knees bent and feet flat on the floor. Extend one leg and then raise your hips up using the strength of the opposite hip only. Hold for 10 seconds and lower. Repeat 10 times on each side. Keep the hips level and in line with your torso. Weakness will show up by one hip jutting out to the side or dipping lower than the other.
Lie on your back, knees bent, feet flat on floor. Lift head and shoulders off the floor and then lower. Keep your neck in neutral and don't pull on your head. Vary tempo. Increase intensity by lifting feet off the floor.
Lie on your back, knees bent, feet flat on floor. As you lift your head and shoulders, rotate your torso to the side bringing the opposite knee and hip towards each other. Then lower. Keep your neck in neutral and don't pull on your head. Alternate sides. Vary tempo.
Lie on your side, legs straight, arms relaxed. Lift shoulders and legs at same time then lower. Vary tempo.
Lie on the floor face down with your arms extended overhead. Using your core lift your arms, shoulders and legs off the floor and fly like Superman then lower. Vary tempo.
Lie on back, press lower back into floor, lift legs with a 90 degree bend at the hips and knees. Curl tailbone off the floor using lower abs then lower while maintaining the 90 degree bend at hips and knees.
Standing Trunk Twist
Hold a stick on your shoulders behind head (not on your neck). Twist torso to one side then the other like a periscope. Keep hips facing forward. No rotation in legs and knees.
Hanging Knee Raise
Hang from pull up bar or dip station. Contract core muscles. Lift knees as high as you can without throwing them. Control the motion while you raise and lower. Vary tempo.