When your boat is not in use
Make sure the boat is firmly secured before you leave it. If you have a pontoon mooring, put out the springs if possible. With a riverbank mooring, don’t just drop a bight or an eye over a piling or a post: if the river floods, the rising hull will simply lift the warp up and off the post and the boat will float free.
The security of a swinging mooring depends very largely on the ground tackle, and if that doesn’t belong to you there’s not much you can do to improve it. However, you can make sure your boat stays attached - put out two lines from the boat to the buoy, and make sure they are in good condition and protected where they may be prone to chafing.
Close all valves on through-hull fittings. Turn off the gas at the cylinder and the electricity at the master switch. (If you have automatic bilge pumps you may want to give them a separate power source, or route their power supply to bypass the master switch). If you need mains electric power for a dehumidifier, bring it directly on board from the shoreline to the dehumidifier, do not route it through the boat’s own AC power circuit.