For going around Spiti Valley, Kaza is ideal base. Having your own vehicle is a huge advantage. Himachal Roadways buses are available from Kaza to nearby areas contact Kaza Bus Depot for details. Local vehicles can be hired as taxies your hotel manager will be of help.
Rickety buses ply the windy mountain roads with varying frequency. Motorcycles are also an option if you on an Enfield tour, but make sure you're experienced and comfortable on a bike before heading up into these rocky high altitude areas. Another option in some areas is to walk between villages, which can take anywhere from a couple hours to a whole day, and is rewarding in its own way.