The first thing is to find out what's causing the sciatica. Infection, disc disease, or tumor are just a few things that can put pressure on the sciatic nerve. Treatment works best when directly specifically at a known cause.
Doctors often start out with pain relievers that also act as an antiinflammatory. This includes ibuprofen, aspirin, and other non-steroidal antiinflammatories. Physical therapy can help if there's a muscle or joint imbalance putting pressure on the nerve.
If conservative measures don't help then your doctor may advise surgery. Again this depends on the underlying cause of the problem. For example, a disc pressing on the nerve can be removed. In such cases, pain relief can be immediate.