N o D i e t | N o A b s
- You cannot out-crunch a bad diet!
Seriously, you can't. The secret to visible abs is low body fat, which you will not get by doing a million crunches. If your diet is not on point, neither will your abs be. - Having a day just to train abs.
If you're doing your other exercises with correct form for example: squats, overhead presses, etc. you are already engaging your core in these movements and you do not need more than 10-15 minutes per day focusing on your abs alone. - Only doing one movement for abs.
Your abdominals are made up of many different muscles in many different places of your core and only doing crunches will not work out all of them. Be diverse in your ab workouts. Try some new stuff.
- Flying through your ab sets.
This is not necessary. Many people look at their abs as one muscle & an easy one to train. Just like your legs, arms, back.. your abs are complex and there are many different muscles to it. Working through your abs like any other muscle (sufficient rest between sets) is necessary.
I personally don't train abs often. I might train them twice a week. Doing my workouts with proper form engages my whole core and gives me a good enough ab workout while training. I eat pretty clean & since doing these things, i've seen huge improvement on that area! Remember that this is a journey to a BETTER you not a perfect you -- it all comes in due time. You must trust that these things are all working together even when you can't see it.