EASY DOES IT It might be easier than you think to save gas. Here's how: "Jackrabbit" starts can burn up to 60 percent more gasoline than normal, gradual grad-ual acceleration. With a manual transmission, transmis-sion, get your car into high smoothly but quickly. At 20 miles per hour, second gear can burn 20 percent more fuel than high gear. Less work for the cook . . .and it's delicious, to boot. That's roast goose, the bird that bastes itself during cooking, thanks to a thin layer of fat between the skin and the meat. The result, a moist, crisp flavorful gourment treat. Look ahead in city traffic: traf-fic: Fewer stops can mean 10 to 25 percent more mpg. Observe the 55-mph limit. For every 5 mph over 55, you can lose a mile a gallon. Combine errands in one trip; a mile in city driving with a cold engine can cut fuel economy as much as 70 percent. But don't waste fuel by "warming up;" it's better to begin rolling smoothly soon after you start. And 30 seconds sec-onds of idling uses as much gasoline as you might use to restart. Under-inflated tires can cost a mile a gallon, and a recent study showed 4 out of 5 tires under-inflated an ' average of 5 pounds.