There are so many ways to strengthen and tone the muscles in your core area, as well as, challenge their endurance for maximum calorie-burn and optimal results.
Even if you're in a rush that day, you can still execute a single move at maximum effort to achieve results. The key is to know which exercises are most productive for you.
Let's take the Russian Twist for example. Watch the video here and review the correct way to execute this exercise. Then, depending on your fitness level, if you're more advance, you can perform 100 repetitions and repeat it 2-3 times. If not, one set of 100 is a good place to work towards.
Whatever fitness level you are, do not rush through this exercise. Take your time and fully challenge your core by executing in an even pace, and fully engaging your ab muscles throughout the entire workout. No swinging, no relying on momentum, no cheating!
Please note: If you have a bad back, a stiff back, or a weak back, you will feel discomfort in your back while executing this exercise. If that is the case, do not proceed with this exercise. Instead, tend to your back issues first by doing back strengthening exercises, specific ab exercises, and overall body stretches, especially in the core area. Even a massage will help. Then, when you're ready, you can come back and try this exercise again.