A pleasant, chatty (if routine) look at some ways to improve our lifestyle. Shimer, editor of the Executive Fitness Newsletter, champions a no-guilt approach; people who have fun live longer, so pleasure is as important as making other recommended changes. His basics fall into three categories. ""How To Keep Bad Habits From Killing You"" advises assessing your fallings--drinking, obesity, stress--and modifying them as much as possible. (""Cigarettes are the riskiest vice of all, but there are ways of improving the odds."") ""Keep Good Habits From Boring You"" offers tips on creativity in diet, exercise, and rest. (Shimer, a marathon runner, is big on that sport.) And, finally, ""How Fitness Fights Disease"" covers--for cancer, diabetes, heart disease (even halitosis and bad skin)--everyday preventive measures. Lightweight--but appealing.