The main Venice planning mistake is treating it like a normal road-based city. Routes depend on walking, bridges and public water transport.
St Mark's and Rialto
St Mark's, the Basilica and Doge's Palace form the main museum block. Continue toward Rialto and the Grand Canal.
Islands or neighbourhoods
Give Murano and Burano a separate block. If you skip the islands, explore Cannaregio and Dorsoduro.
Transport
A short-looking map distance can involve bridges and detours. Check the current vaporetto network before travelling.