What is the best way to get from Sorrento to Positano?
You coudl take a Sita bus, there is one about every one hour or an hydrofoil for the schedule have a look on www.metrodelmare.com.
Otherwise you could take also a taxi and the price is about Euro 50.
The sita bus is regular, convenient and cheap. You can get the bus from outside the train station. Tickets have to be purchased before travel (they can be bought from the newsagents at the station) and must be validated on the ticket machine on the bus. This can normally be found just behind the drivers seat. Try to sit on the side of the bus at the door (not the drivers side). You will get the best view of the fantastic coastline this way.