If you're looking for an easy oblique exercise, try the side crunch. The oblique muscles are used to assist with rotation of the torso, as well as basic abdominal contractions. It is important to note that even though the side crunch is an oblique exercise, the entire abdominal region is being worked.
The side crunch is done from a supine position (on your back). Once in place, cross the knee opposite the oblique muscle you wish to work. For example, if you want to work the right side, cross the left knee. The right hand goes behind the head, while the other is out to the side for stability. Crunch the oblique muscle by moving the elbow across the body toward the knee. You should reach with your elbow and try to touch your knee. Exhale each time the elbow approaches the knee. Perform several repetitions on one side before switching to the opposite side.
Lie on back. Cross knee. Hand behind head.
Crunch the oblique muscle by moving the elbow toward the knee. Exhale.
Slowly return and repeat the exercise.