Getting a lean six pack is hard work, no way around that. There are so many stratagies to build a ripped core but one of the most effective ways is the combination of ab work with high intensity cardio such as farmers walks or sprints.
Supersetting crunches or any traditional ab exercise with a weighted carry or high intensity movement like sprints will work the abs in a new and effective way - The cardio gets the blood pumping, while following it up with an ab exercise pushes all that blood to the abdominal area. This extra blood flow to the area aids in dropping that last bit of fat to uncover your much wanted 6 pack.
A workout could look like the following -
farmers walk - as heavy as you can go for 100seconds
Leg raises - 60 seconds of work
repeat 4-6 times.
simple! The leg raises can be replaced by any ab movement while the farmers walks can be replaced by any high intensity cardio exercise like sprints or rowing.
this workout is best performed on a non lifting day but can, if pressed be done at the end of your regular lifting session.