High aspect ratio microstructures are frequently made with the Lithographie, Galvanoformung, Abformung (LIGA) process. The success of this process depends critically on "deep" X-ray lithography (DXRL). This paper presents a variety of experimentally and analytically determined techniques for optimizing DXRL. These include methods for designing and fabricating high-quality X-ray masks. Methods for optimizing the exposure dosage and developing cycle are described. New methods for promoting resist adhesion and for avoiding resist film cracking are discussed. The influence of developer surface tension on the resist solvation process is quantified and new methods for controlling this surface tension are described.