An effective way to tighten and strengthen your abdominal muscles is to perform the traditional abdominal crunch exercises. They are very versatile and convenient as they can be performed basically anywhere whether it is lying flat on the floor, using a Swiss ball, a weight lifting bench, or an abdominal exercise machine. If you already have the above exercise equipment that I just mentioned then, use them to get started. If your just starting out it is better to start slowly with the floor crunch exercise because it is the most safe and effective way to place your core abdominal muscles.
To get the best performance you need to do 15-20 reps of each abdominal exercise. You can build up your abdominal muscles by doing a veriety of abdominal exercises with and without weight.
Even though the traditional crunch or sit up exercise is very effective most people find it quite strenuous to do. They avoid doing them because they complain that both their neck and back become strained and painful. The problem isn't the crunch exercise but the way people perform it. Most people use the wrong technique and that is the leading cause of why they strain their back and neck. The proper way to do the crunch is to lay flat on your back keeping your elbows back and open.
Do not be tempted to pull on your head and neck as you come up as this creates the strain to that area. When you pull on your head and neck this takes resistance and focus away from tightening your abdominal muscles. The tendency to pull your head and neck forward as you do the crunch is due to your weak abdominal and back muscles. At the moment these muscles don't have the authority and strength to provide you with the control to pull yourself up without reverting to your arms pushing on the back of your head.
As your starting during the first time do the crunch slowly. Focus on tightening your abdominal muscles as you raise your head and curl in towards your knees. Rise in to the curl slowly and avoid any quick jerky movements. When you feel your hands pushing against the back of your head and neck then that's the sign to halt and take a break. In the beginning it will take time before you can do 25 to 50 crunches. At this point focus on getting the technique right. Focus on quality not quantity as 10 perfect crunches is valued at more than 50 poorly performed crunches.
When you can easily do 50 perfect crunches you can try to do more challenging crunch exercises by placing a secured weight on your chest or perform decline crunches on a weight bench.