A few years ago I was involved in producing a book about the town where I lived at the time.  I was lucky enough to have my work published in the book but I was frustrated because I knew that more of my photos could have been included if I has thought harder about how my images could be used at the taking stage.  I realised that before I release the shutter I have to think about how the photo might end up being used.  The biggest lesson was to realise that when editors create pages - both on the web and in print - they have to think about the overall layout of the page.  Sometimes they will need a landscape image and sometimes a portrait version.  My biggest mistake all those years ago was to make the best photograph whether it was portrait or landscape and only shoot that version, these days I shoot both.  That way, if an editor likes my work they can choose which version will fit their page.