Work Your Core First

It has been seen that people achieve far better results when they do core exercises at the beginning of their workout instead of at the end.  The reason is that when training your core when your muscles are fresh you achieve the fastest gains in strength.  Focus on core strengthening exercise that allow you to prevent your spine from rounding, such as planks, mountain climbers, and even push-ups.  These type of exercises allow you to not only strengthen your stomach muscles, but also you side and lower back muscles.