I don't know if this is "Recomended" but my method has always to use plenty of water and simply wash ! A good branded "Car shampoo" is useful for getting the really grimy stuff off. One tip I will pass on is to try and get hold of one of those "Micrlofibre" towels (they look just like a hand towel) usually bright yellow in colour. They are excellent at drying off.
Life begins at Forty !... I was born with nothing, I seem to have most of it left.
2002 Titan Silver BMW 316ti Auto Compact
2000 Bright Green V.W. Golf Avantgarde Cabriolet
1989 White V.W. Golf Cabriolet (G.T.i.)
1968 Anchor Blue Cortina 1600 GT