Hi,

Depending on the cause of pain there are several specific sciatica exercises... You can have a look at the "Sciatica Exercises" which i have posted earlier on.
For herniated discs, extension exercises that arch the spine backward rather than flexing it forward provides more relief. As for spinal stenosis,flexion exercises are encouraged more,coz it increases the size of the passageways and allows the irritation or impingement to resolve.

Cheers!!