THE SUN MAGAZINE IS LOOKING FOR A FEW good idea from its readers on how to make Baltimore a better place. We plan to publish the best ideas in the first issue of 1991. Ideas -- in 200 words or less, please -- may range from whimsical to serious. Send your typewritten suggestions, postmarked no later than Nov. 30, to Making Baltimore Better, The Sun Magazine, Box 1377, Baltimore, Md. 21278. Please include your name, address and daytime phone number.