Maintain an abdominal "brace" (remember, not a hard contraction) and breathe normally throughout the exercise. Lift the hips until your body is straight. Hold the position for as long as you comfortably can, starting with about 5-7 seconds and working up slowly.
As you get stronger, you can increase the challenge by lifting one foot at a time about 1-2" off the floor (not higher). When you do this, focus on keeping your pelvis level and your torso very still.