Stability ball abdominal roll-outs are a nice exercise to challenge the anti-extension muscles of the core. Stability balls can be a bit unstable for the newbie, so there is a bit of reactive core training involved with this exercise.
As with any exercise, work these consistently until you're able to execute 10-12 repetitions with ease. Once you're no longer being challenged, lower the hands closer to the floor by using an ab wheel, suspension trainer or gymnastics rings for the next level of difficulty. This will change the training stimulus, as your chest will now be parallel to the ground surface, requiring a larger contraction from the core to maintain body position.