Carb must be dry. Best to empty the tank as well, but you can always dump the tank later. I like to to take out the plug and dump a little Marvel Mystery Oil in the cylinder, then turn it over a few times.
Very important: After the plug is back in, turn the engine over until you feel compression. Closing the valves does two things: It keeps moisture out of the combustion chamber, but it also helps to prevent the valves from sticking open.