In the last live session tbere was a question about when to change the guitar strings. I wanted to give some suggestions of how to get more life out of the strings before you have to change them. Firstly, I recommend buying Elixir nanoweb acoustic guitar strings which are coated and give a longer life. Secondly, as Tomas mentioned, the oil and acid in the skin of the of the fingers is what causes most of the corrosion. I found that if I use a silver cleaning cloth like that which is used to clean jewelry, and clean the strings and fret board after every use of the guitar or at least once a day, there is hardly any corrosion at all. Of course the strings will wear out eventually, but the time is extended by many months.