Mcclintock gives the rules for some 40 games ranging from Cricket and 301-as basic to darts as 7-card stud is to poker--to the very demanding Mulligan. But more important than rules--which can be adjusted or improvised-is etiquette and the ""sianguage"" of this English pub pastime newly popular among Yanks. Civility prohibits using another man's darts and commands silence while a shot is being made. Once you've thrown against, say, Conrad Daniels, the top-ranking US player, you shouldn't feel too bad if you land in the wrong bed or whitewash. He might respond with a gracious, ""Muggs away"" and sooner or later, with posture and concentration perfected, will come the thrill of a cork.