Cold packs on your lower spine.  Heat seems to increase the inflammation, although I have heard of people using ultrasound... There are also some exercises which may help, if you can get help from a physical therapist or a chiropractor.  And ... rest.  If you're in pain (shoveling snow or whatever), stop if you can and rest. Sometimes that's easier said than done.

Supposedly most sciatica does eventually go away by itself.  I'm 58 and I've had it  a couple of times.  There is also something similar called piriformis syndrome, for which there is a specific exercise.  If the sciatic nerve goes through the piriformis muscle, then when the muscle contracts, it can irritate the nerve.  The exercise can be done lying down or sitting, but it's supposed to be better lying down.  You bend the knee on the side of the sciatica, and bring it up over your other thigh (not everyone may be able to do this ... use caution), then gently press down on the bent knee.  This did help me when I had piriformis syndrome.  It didn't help when it was just plain sciatica - but the sciatica did eventually go away.  Good luck!