Bankers don't often open up--so Cook's instructive tips, set against recollections of his 15 years with the ultra-Establishment Bank of New York, rate a small, discreet celebration. Banking, he says at the outset, is an over-regulated industry ""without a dime's worth of difference"" among copycat rivals. Institutions compete nonetheless, in particular for retail accounts which represent a cheap source of funds for the lucrative commercial and consumer loans that are management's true preoccupation. Retail service is an expensive proposition, however, so banks are reluctant to provide any more than they must. To become a preferred bank customer--entitled to overdraft privileges, investment services, no-charge estate planning, introductions, etc.--he suggests securing a referral. Once in the door, aspirants should try to make themselves appear prospectively important and, at the same time, instill confidence which can be drawn upon in time of need. Tracing the course of a signature loan application, Cook notes that what really counts, apart from an acceptable credit report, is gross income; banks are reluctant to advance more than 20 percent of this figure. Few check, though, so it's safe to fudge upward. Also covered are: the varieties of retail loan (demand, automobile, mortgage, small business, etc.); consumer-protection measures; and banking-Establishment attitudes toward women, gays, blacks, Jews, and members of other minority groups. (Only the laws have changed, says Cook.) Frank and down-to-earth.