Getting around Spiti requires either your own vehicle (motorcycle or 4WD) or a combination of shared jeeps, local buses, and walking. Kaza is the hub: buses from Kaza serve Tabo and the lower valley, and shared jeeps fill in the gaps. Hiring a vehicle in Kaza for a day costs roughly 2,000-3,500 rupees depending on the route; this is by far the most efficient way to hit multiple destinations.
Motorcycles are popular with experienced riders — the roads are rough, the distances manageable, and the freedom to stop anywhere is significant. Bikes can be rented in Manali. Walking and trekking connects many of the higher villages, including the Hikkim-Langza-Komic circuit, which can be done as a half-day walk from the road.
Altitude is a serious consideration. Kaza is at 3,800 metres, and the villages and passes above it go to 4,500-4,600 metres. Take a day or two to acclimatise in Kaza before heading higher, and watch for symptoms of altitude sickness — headache, nausea, difficulty breathing — which warrant immediate descent. The Spiti Ecosphere office in Kaza is a good resource for logistics and local guide hire.