There are several types of japanese gardens but all rely on the concept of wabi-sabi (see my post on "rules for placing stones" below). If you cannot achieve the proper wabi-sabi, you will not be able to have a convincing japanese garden. It must convey this 'feeling'; it cannot be achieved simply by the use of japanese plants and ornamentation. Read books by David Slawson and Peter Keane; also japanese writers Itoh, Katsuo Saito, Kiyoshi Seike, and Tatsuo Ishimoto. If your local library does not have these authors, you can get their books by use of the interlibrary loan. You will find that many of the older books have better garden technique descriptions while the later books have the better pictures. You can get good buys on used editions on ebay and amazon. Remember, stresss quality over quantity and keep it simple!