A basement is not a good place to store materials you want to last. Keep it out of direct sunlight. Direct sunlight is especially damaging to photographs, but it can also fade printed matter and handwriting, make paper deteriorate more quickly, fade the color from fabric, and so on. Keep it cool. Heat can damage or destroy materials such as written and printed matter.
Heat is especially damaging to audio and video tape.
Paper Most paper has a certain amount of acid content that causes it to deteriorate over time. Acid-free paper, as you can see in the better books of the Nineteenth Century, retains its white or cream color and remains flexible. Archives and libraries preserve material on perishable paper by photocopying it onto acid-free paper. You might want to do this yourself, if you have paperwork that is in danger of crumbling. Color photographs also last fairly well, but the dyes used to color them fade more quickly than black and white.