The sciatic nerve is the longest nerve in the body and starts at the base of the spine and runs down through the thigh and calf muscles of each leg. Pain can be caused from a herniated disc in the lower lumbar spine or more frequently by a tight piriformis muscle (the small muscle located behind the gluteus maximus). I would recommend a gentle yoga practice that focuses on opening the hips, stretching the hamstrings and releasing the piriformis.
In cases where sciatica is due to a tight piriformis, the focus of the practice is on opening the hips and stretching the hamstrings. I would also include some poses that strengthen the lower back, in case the sciatica is caused by a herniated disc.
Below is a gentle series of stretches to open the hips, stretch the hamstrings and lower back:
(1) Easy Pose (Sukhasana) – a gentle hip opener to start off with that people with sciatica may find challenging – exhale and bend the knees and crossing the ankels – hold for five breaths - use blocks or blankets under each knee if tight.
(2) Bound Angle Pose (Baddha Konasana) – Exhale bend the knees and bring the heels towards the pelvis, pressing the soles of the feet together and holding for five breaths – a gentle pose that opens the hips.
(3) Standing Twist for five breaths – Standing with one leg against the wall, bent and on a chair and the other leg straight – Gently twist towards the wall as you exhale, keeping hips level and hands against the wall/facing towards the wall.
(4) Standing forward bend (Uttansana) for five breaths – stretching the hamstrings can help relieve the pain associated with sciatica.
(5) Downward facing dog (Adho Mukha Svanasana) for five breaths – aligns, lengthens and strengthens the lower back, which is particularly important for sciatica caused by a herniated disc in the lower back.
(6) Half Spinal Twist (Ardha Matsyendrasana) for five breaths – twist very gently as going to fast too soon can instigate sciatic pain. This stretches the piriformis in the hip and encourages it to release/lengthen.
(7) Cow's face pose (Gomukhasana) – opens the hips and releases the hamstrings – hold for five breaths. Beginners can bend only one leg over the thigh and keep the other leg straight.
(8) King Pigeon Pose (Raja Kapotasana) – Stretches and releases the piriformis – beginners can use a blanket under the hip – hold for five breaths
(9) Finally Relaxation - Savasana for 5 minutes
(10) Meditation - seated meditation starting with deep full belly breathing (10 breaths) and then just watching the breath for a few minutes
I would also recommend strengthening exercises such as low impact cardiovascular exercises such as walking or swimming. Also be sure to drink plenty of water and eat a healthy diet.