A toned stomach can be achieved by training the body as a whole unit. There is a mis-conception that doing sit ups or crunches will give you a flat stomach - it won’t! We cannot ‘spot’ train any one part of our body.
Whilst these excesses can be layered into a training programme to compliment other exercises, I would not recommend them for optimum fat loss and muscle toning around the stomach area.
Use a combination of lifting, pushing, pulling, squatting and movement-based core exercises that challenge the body in different movement patterns to help flatten and tone the stomach. Consistency is also key for body fat loss and muscle building in any area of the body.
Adding in interval training will also help to increase the metabolism and burn calories with the heart rate very high, which has amazing fat loss potential!
So, in short, combining resistance training for the whole body, along with good nutrition and some interval training will most definitely get you on your way to a flatter tummy!