Rajsamand town is compact enough to walk between the main sights. The Nauchowki embankment, the Dwarikadhish Temple, and the lake ghats are all within easy reach of each other on foot. Auto-rickshaws are available for short hops within town and can be hired for a fixed rate if you want to explore the lake's more distant shoreline.
If you are combining Rajsamand with a visit to Kumbhalgarh Fort (about 50 km northwest) or Nathdwara (17 km south), a hired car or taxi is the most practical option, as local bus connections between these places can be infrequent.