Keep the hands at a distance away from the spine that does not strain your spine but just mildly stretches it.
Always look inside your body and ask it how far it wants to progress into a displayed stretch.
Entering Cobra pose mildly really helps the spine but don't be tempted to over-stretch.
Come into mild resistance so that it feels good on your back and hold.
If it's hard to hold try coming down and then back up to Cobra pose. | 
