You can train your ABS all you want, but if your diet isn't in check, you'll never see that six-pack. 

I train my ABS 4 times per week at the end of my workout session.  Currently, my ABS is still not quite visible yet because of my body fat.  However, my mid-section is getting tighter as days go by because of better diet control and proper abs workout routines in recent months.      

In terms of ABS training and advises, the following articles pretty much sums up for you! 

http://www.bodybuilding.com/fun/10-ab-training-mistakes-you-need-to-stop-making.html

http://www.bodybuilding.com/fun/ab-training-6-reasons-your-abs-arent-showing.html