Mistake #1 - You have no intensity in your ab workouts
Don't get me wrong, it's hard to do hundreds and hundreds of crunches in an ab workout and you can get a burn in your abs, but that doesn't mean the ab workout is intense. What you need to do to get more 6-pack abs results in less workout time is to increase the intensity of the ab exercises you use.
For example, most folks do hundreds of crunches in an ab workout but don't get results. On the other hand, if you increase the intensity of the ab exercises you use, therefore decreasing the number of repetitions you can do in each set, you'll put more stress on the muscle and force more change in your abs.
So get rid of the crunches and add exercises like Stability Ball Rollouts to your ab workouts, which you can't do hundreds of times. Get rid of lying reverse crunches and use hanging knee raises - with good form - instead and do sets of 8-12 repetitions rather than sets of 30-50 reps.
Mistake #2 - Doing Too Many Reps
There is no need to do 50, 100 or thousands of crunches each day. Many people do more, thinking it will help them spot-reduce (lose fat) from the belly, but that is a myth. In fact, if you are doing your exercises correctly, 8-15 repetitions are all that you need to target those muscles and get results. Here's an easy rule: Train the abs like you would any other muscle, which typically involves 1-3 sets of 8-20 repetitions per exercise.
Mistake #3 - Believing in Belly Fat Burners
Can specific foods, nutrients, diet pills or supplements really target belly fat and help you melt it away? Probably not. There is some research to show that certain nutrients may help people lose more belly fat, but most of this "research" is sketchy at best—poorly controlled, poorly designed, and not well replicated. It'd be nice to think that you could just eat an exotic berry or pepper—or pop a pill that contains them—and melt away the inches from your waist, but don't fall for this hype. The person telling you that any food or product can burn fat from your belly has one goal in mind: selling you something. If it sounds too good to be true, it probably is!
Mistake #4 - You do not brace your abs in every exercise
When training clients, I tell them before each and every exercise to "brace their abs as if someone was about to punch them in the stomach". Bracing your abs protects your back, and also works your abs, so that every exercise in your workout becomes an ab exercise and every workout becomes an ab workout. It is a simple, easy to remember tip that will help you strengthen your back and sculpt your abs.