Stand carefully on the twist board with your feet together and your posture completely erect, doing nothing more complex than attempting to maintain your balance. It is important that you become comfortable just standing on the equipment for a time to minimize your risk of injury when you do couple the twist board with active exercises, so become familiar with the nuances of the board for a day or two before moving on to more advanced drills.
Perform a basic twist by bending your knees slightly and pivot your posture to the left until you are at a 45 degree angle. Keep your torso upright throughout, with your head held high and your chest out. You should feel a contraction in your obliques -- on the side of your torso underneath your ribs and above your hips -- as you turn to the left. Hold in the position that affords you maximal contraction for a period of one to two seconds before returning to the neutral "straight-ahead" position. Repeat to the other side, performing two or three sets of eight to ten reps per side.
Perform an advanced twist with resistance by holding a light medicine ball in your hands -- held against your chest/abdominal area. Twist to the side until your body is at a 45 degree angle, generating a contraction in your oblique and holding the position for a second or so before returning to the neutral position. Perform two or three sets of six to eight reps per side. Start with the lightest medicine ball that your gym has -- usually five pounds -- and increase the weight as you get stronger.