With major West End musicals now routinely costing untold millions to bring to the stage, it’s become more crucial than ever to have an idea of what is likely to result in success before one begins. Thus, the rules: “If you can’t sum up your £10 million spectacular in a breath, forget about it… Exude a winner’s confidence before you even open.” And if you want a long run, “people have got to come more than once.”