Get one of those little gold thingys that has the copper-colored mesh in it (Hakko 599B). Use it to clean your tip during while you're working. I also first go over pins to be desoldered with the wire brush on my Dremel tool in order to remove dirt and corrosion. Seems to make desoldering quicker and keeps your tip cleaner. And don't forget to put a blob of solder on the tip before you shut it off to prevent rust.