If you suffer from back pain then before embarking on any specific type of exercises you should consult your GP first.
Some of the worst ones you can do which could aggravate or even worsen your condition are toe touches. They can put greater stress on the discs and ligaments in your spine. They can also overstretch lower back muscles and ham strings.
Avoid sit ups, as they may also put a lot of pressure on the discs in your spine.
Finally, left lifts should also be avoided as they can make your back pain worsen.