Low back is very huge subject, and it is very hard to fit everything in one basket and provide one or two exercises for everyone.
If you are interested in reading more about Low back Pain or Sciatica, please read my blog on low back pain which might help you understand what back pain is and how can you manage it easily.
In my clinical practice what I have seen one exercise which helps most of my patient is sloppy push up, if you have back pain and you want to do some exercise this is the first exercise everyone should try but for any reason if the pain increases after the exercises you should stop the exercise and consult your family physician or physiotherapist.
First exercise: Prone exentension
Second common exercise which helps my patient is: standing extension.
Third and most common exercise which helps my patient is: Double knee to chest.
DISCLAIMER: This is not meant to replace medical assessment/treatment. Please see your physician or physiotherapist to get a customised plan for your low back pain.
Before providing exercise to my patients, I perform a thorough assessment and then prescribe appropriate treatment modalities/exercises.