Abdominal exercises are generally unique in that they involve a variety of zones: the body, hands, and feet.
Many athletes set a goal to increase the muscles, to increase them in volume. In this case, you need complex most effective abdominal exercises: lowering the legs lying down or lifting the legs in the vise. But most people, in order to achieve simply a beautiful embossed abdominal, it is enough to do light exercises with a lot of repetitions. Working on exercise for abdominal muscles, we burn fatty tissue not only in the abdomen but in the whole body.
As for the technique of performing exercises, it should be noted that all training for the abdominal muscles needs to be done while breathing out and drawing the stomach into oneself. This will improve the effectiveness of each exercise routine.
Do not watch the number of repeats performed; rely only on your feelings. At the moment when you begin to feel your muscles (the way they are tense and how they work), then just start counting the number of repetitions in your approach. You can do 5 sets of 20 repetitions, and you can have 3 sets of 15. And most likely, the latter option will be much more effective for your muscles, since in this case you were maximally included in the process and did not let your muscles relax.