The best suggestion - shop around. This year I was able to get a scooter for 200 kn for 24 hrs. A specialty food store in the market place, near St. Stephan, has scooters to rent - pick up some cheese , sausage, anchovies and a scooter and search out a secluded cove.
Most scooter rental are near the bus station which is behind St. Stephen.
My only other suggestion - get out early so as to see the morning light bouncing off the water