I'll add my own secrets here. Before I clean the soundboard of my grand, I take a wad of steel wool and gently swipe--not rub-- the top side of the steel (not the copper) strings. Why? In places where there is summer humidity, minute rust particles can form there and weaken the strings.
So you say, "that's interesting, but get on to cleaning the soundboard. I don't dare to try it." Two generations ago, women wore corsetts which had long corsett bones. I had one of those old bones passed on to me by an enterprising piano tuner. I won't divulge how he got it. Anyway, it's a flexible tool. I drop a dust rag at the flat side of the soundboard. I can then poke the flexible corsett bone right through the strings anywhere and move the dust rag around with total ease right up to the top of the treble. Getting the rag back to its starting place and out is a breeze too. You're probably envious, but, hey, you have to know all the tricks.
