I only train abs 1-2x week. I use alot of added resistance with mine. decline crunches with plate on chest, cable crunches, hanging leg raise w/db between feet, reverse crunches w/db between feet. If I do any work for obliques such as twists on the decline it will be strictly my bodyweight.
With ab training more is not always better. Concentrate on contracting your abs to carry out the movement and squeeze at the peak of movement and then slowly let your abs bring you back to the start.

I think ab training is trial and error for everyone at first, to determine what works for you.

I do core training 3x a week. Breaking them into 3 core sessions...3 sets X 20-25

Session 1 - Cable Crunches to the Front, Cable Crunches to the side, Decline Weighted Crunches, Weighted Obliques Twists, weighted back extensions.

Session 2 - Bicycles, Ball crunches, Oblique Twists, Planks and Side Planks.

Session 3 - Bicycles, Reverse crunches, Hanging Leg Raises, Cable Crunches, Decline Twist Crunches and Planks, and ball back extensions.

Great advise!! Much needed might I add! hehe

I train abs usually three times a week. I do them when I do my heavy bag workout. I do reverse ball curls, hanging knee raises, medicine ball ab work. With my obliques, i never use weight. I do oblique crunches and crossover crunches. I also don't believe in counting the reps. I just do them until I can do no more.....lol

i love using the roman chair for knee raises.