Work your abs 2-3 non-consecutive days a week, taking care to target all your ab muscles.
There are some great ab specific excercies out there and it is also good to incorporate core specific or engaging excercises with your other training. Also, for those doing the Fitness Contest, be sure to incorporate just the standard situps.
Here’s some links to other good ab workouts:
http://www.bodybuilding.com/fun/bbinfo.php?page=Abdominals
http://exercise.about.com/cs/abs/a/strengthenabs.htm
