Avoid dusty and moist areas. Dust gets everywhere, and moisture makes fungus grow! Unfortunately my darkroom is plagued by both dust and fungus. There is probably something I could do but it would involves alot of work in remaking the floor and rendering the walls. The floor is concrete and when it rains moisture seeps into the room and after a month of not using it I had fungus growing on my paper boxes and also inside the box

I have a question for others, how do you stop light reflecting off the paper hitting the walls and coming back to expose the paper again. Is a black cloth around the enlarger the usual thing to use?