Many years ago I went to a photoshop conference to try and get better. There was a talk about converting color photos to black and white. As a former bw film photog this interested me. Black and white film is a little wierd (some people put red filters on the lenses to increase contrast)
He showed some techniques. I think someone asked a question about the best way, but the presenter got a little ranty and basically said the way that looks best to your eye is the best way.