New guitar strings sound bright and loud, but the oil and sweat from your hands, along with air, can oxidize the strings. When the strings become discolored or sound dull, it's time to change them.
Marty says you can extend the life of your strings by washing your hands before you play guitar and by wiping the strings with a dry cloth after each practice. For maintaining a good sound, it's best to change your guitar strings ever couple of months, depending how much you play.
Marty uses D’Addario J16 acoustic guitar strings and recommends them for their great sound and durability.