To travel within Palani, there are many buses, autos and cabs. If hiring a cab, then it is better to enquire with more than one travel agent/ cab service before finalizing on a cab. Very often the cab drivers are quite informative and offer to guide you. It is better not to seek their help to take you to shops.
You can hire a car or take your own to Palani. The approach roads are good. Equipped with a road map, it is easy to drive down. However if going from Chennai, it is better you take the plane or train or the overnight bus. The bus being the last option due to the tedious nature of the drive.