Over the years i have collected numerous books, and inherited many more from my grandfather that are well over 100 years old. Most are still in suprisingly good shape. What is the best thing i can do to preserve their quality for the longest time possible?
I’m not an expert, but my thought would be to keep them in a cool, dry place away from light, and not to handle them often. If you’re really worried, you could wear gloves when you handle them to keep the oils in your hands from harming them. And make sure no insects are around to chew them up.
As a side note, if you have any newspapers you’re worried about, I recently called a conservator to ask how I could preserve a newspaper and she told me it’s a losing game. Newspaper is made to disintegrate and it will, eventually, no matter what you do. But basically she told me the things I already mentioned, and also to keep it folded the way it came and not to frame it.
There is a discussion illinoishistory.gov well sumerized by carter6 above. Additionally they say keep them away from circulating air as this has dust and cleaning materials. At the University of Alaska we kept older materials of value in a somewhat dimly lighted room in cabinets with locked sliding glass doors. This allowed some viewing but required special handling if the patron wanted to touch them.