For start, I will remind you that there is no such thing as burning fat from one area only. Doing hundreds of repetitions of crunches will not make your belly have less fat on it. The factors, which influence body fat reduction are, most of all, diet and strength, aerobic or interval training.
Abdominal muscles training does not reduce fat from that area. However, it helps to strengthen those muscles and make them visible.
Opposite to what majority of women do when it comes to the abs workout, i.e. lots of repetitions in various positions in supine position, abdominals react perfectly to large load and low range of repetitions. So, forget aboout doing 200 crunches every day.
So what is the best way to train abs?
First of all, using multi-joint exercises, such as squats and deadlift. Such exercises, especially if they are performed with large load, are effective training for rectus abdominis, obliques, deep muscles and back muscles.
Take most of your time for multi-joint exercises in your training plan. Thanks to that procedure, you will engage abdominal and back muscles to work, and you will also burn much more calories than during doing crunches.
Second of all, find some space for balance exercises, such as plank, in your training plan, which you can perform in many variations. At the beginning, do such exercises without any additional load. After some time you can add some load, but it shouldn't be too big.
Third of all, you should also include such exercises, as leg lifts, cable crunches, woodchopper or russian twist.
Do those exercises at the end of your gym workout in the range of 15 repetitions in one set.
You just need to pick one or two exercises per session and do two, at most three, sets of it. Loading abdominal muscles too much will not bring better results. You should also not train abs every day, because you may overload them. At that time your spine will not have enough support from the muscle corset.
It's very important not to omit the exercises, which engage back muscles. It's the easiest way to cause disproportion. The disproportion between abdominal and back muscles may result in backache.
To sum up, the best workout for abdominal muscles is strength training based on multi-joint exercises, such as squats or deadlift. It's good to include also other exercises, such as plank or leg lifts, in your training plan.