Tips For Reducing Fuel Usage

Slower speeds on the water will reduce use
The proper use of trim tabs reduces drag, especially while accelerating up to planning speeds.
Minimize the amount of time that you idle at the dock
Minimize the use of onboard generators.
Use dock-side electrical power in lieu of generators.
Have a float plan so you know exactly where you're going.
Make sure the hull is clean.
Don't under-power your boat. It's important you have enough motor to handle the load.
Check your propeller. If your boat is slow "out of the hole" or lacks top-end speed, you might have the wrong propeller.
A well-tuned engine uses less fuel.
Use the grade of gasoline specified by the engine manufacturer.