The creative benefits of guided imagery and creative visualization have been well documented. Make sure that when you come to the computer to do a guided imagery that you are comfortable, that you have some music playing or perhaps a candle burning. Before you start open Microsoft word and then minimize it, ready for when you have finished absorbing the scene.
Relax and try to visualize yourself being a part of the scene. Once you have finished reading and absorbing the scene simply begin to write. Do not try to control the outcome. Simply write.