R.J. Turner has mastered that favorite Washington game. buying and renovating old houses. And now he is sharing his game plan in a book, How to find a House to Renovate in Washington, D.C. The book is more interesting than its title, and would be useful to read before you buy any house, whether or not you think it needs renovation. It suggests the best times to see the worst aspects of your potential neighborhood, and what to look for during those times. It explains not only how to find houses you might like to buy, but also how to find the owners of those houses. And once you are actually looking over a property, it tells how to evaluate everything from the front stoop to the roof. It differentiates between flaws that are important and those you can safely overlook. One chapter is devoted to systems: electrical, plumbing and heating. On goes the book to how to relate to the zoning commission, how to find a good lawyer - even naming names - and how to finance that house. Leaving no small matter unattended, it even tells how to buy wood for your new fireplace. Written with considerable wit, it is far more fun to read than the real estate ads and contracts and mortgage bills that become required reading when you are house hunting. How to Find a House to Renovate in Washington, D.C. by R.J. Turner. Turner Publishing. $4.95 plus fifty cents postage, from Turner Real Estate, 325 Pennsylvania Ave. SE. Washington, D.C. 20003. Also at some book stores and hardware stores. 546-8747.