For most people, paying for almost any kind of insurance is one of those necessities they would rather do without. But they understand why they need it. Beyond that, there's not much about the insurance industry they do understand. Mr. Tobias's examination of this multibillion-dollar business is witty and clearly written, if sometimes a bit cynical. He looks at how the industry writes life insurance as well as at its coverage on autos, homes, and personal property. He examines the industry's accounting practices, why prices on the same coverage can vary so much, how the firms market insurance, and other things most insurance salesmen won't tell you. In this generally useful consumer guide, the most valuable part is only 25 pages long, a chapter on specific buying tips titled ''How to Buy Insurance.''