I experienced a bit of sciatica when we were doing our cross-country road trip this summer and would do a little yoga in the hotel room each night. One of my favorite poses to relieve sciatica is supta gomukhasana (aka reclined cow face pose, which is a weird name that I don't understand at all). Anyway.
There are two ways to do this pose. If you've got limited flexibility, grab the tops of the shins rather than straining to reach the feet. This modification is shown in the video below. If more flexibility is accessible to you, then go ahead and do what's shown above.
The biggest tip I can give is to find your edge and stay in the pose for as long as feels good before taking it over to the other side.
If you still feel like you need a bit more to relieve your sciatica, try this yoga video for legs and low back. Hope that helps!