Planks are an awesome exercise for core, hip and shoulder strength and stability and a plank on the TRX will be even more challenging and effective for the core as it works to stabilize the body.
Begin by adjusting your TRX to mid calf length.
Then put your toes in the straps and roll sideways onto one forearm. Be sure to keep the elbow directly under the shoulder to protect the shoulder and the top foot should be in the forward position.
Begin the hip dip by dropping the hip to the floor and back up. Then thread the top arm under the body to twist the body and work the obliques. Alternate between the hip dip and the oblique twist for maximum core stability and strength.
Be sure to repeat an equal number of reps on the opposite side to keep the body balanced in both strength and stability.