Has mildew and dirt left your siding less than lustrous?  A soft cloth and long handled brush might be just the tools you'll need to bring back the shine.  For starters mix up some mild household cleaners like Fantastic, Lestoil or Spic-n-Span.  This will clean most of the siding.  Follow up on tough spots with a mild abrasive like Comet or Ajax.  Be careful not to apply too much pressure on the siding or it could be damaged for good. Never power wash vinyl siding.  The strong streams of water can pierce through and leave your siding looking like a sieve!