Abdominal workouts are the most common but are often not worked out properly. The

Abdominal workouts are the most common but are often not worked out properly. The reason is because you actually have four zones of abdominals and different movements will hit different zones. See the diagram below

Most people end up of working out the mid abdominals only. Lower abs are usually hit by incorporating legs, upper abs by a reaching or arm movement, and obliques by turning. Check out some of these videos and get some ideas to create your own ab routine. Make sure you target each zone. More advanced students can also add weight at the legs or holding above your head for added difficulty. For holding a weight above your head, it should remain above your head at all times and you should never use the weight as momentum, common mistake.
https://www.youtube.com/watch?v=svdPTfOpAyQ
https://www.youtube.com/watch?v=flCgEGVCtQ8
Assignment: Try out these ab workouts one day at the end of your work out. You always do core at the end. Create your own ab workout to finish out your total body work out. You should have 6-8 exercises picked that target all of the zones. Also many ab exercises have ways to make them harder as you combine and add weight.