You can flush your engines, as well as add gas treatments to ensure your center console is running right. With that being said if your boat has been sitting for a while with a lot of fuel in it, before running the engines add some fuel treatment to it. Most importantly, routinely draining or changing your Fuel/ Water filters can ensure flawless engine performance. Flushing your Engines with freshwater after regular use is also very important. You can even put a drop of soap in your flush hose. A lot of people are afraid to wash the actual engines themselves but it probably helps more than it can hurt. Whether you have inboards or outboards, give them a light freshwater spray and let them dry well before starting again to insure no wet electrical components. Let them dry in the sun or do it in a warm engine room and then hit them with a light coat of aerosol silicone spray or lubricant after they dry. Once a month or before the boat will be sitting for a while is a great habit.