Software defect / error prevention and software quality have been constantly improved over the past years, e.g. by applying various methods and measures and using modern programming languages.As the complexity and the scale of the software (SW) that has to designed are continually growing, it is necessary for the software quality to keep in step with this development. However, keeping in step is not enough because software applications are used more and more in security-related areas where e.g. human lives are at risk.One aspect of a further optimization of SW quality therefore is the determination of the success criteria that lead to a further prevention of errors. This prevention of software errors is especially important in the initial phases of software development.The following text therefore shows the essential success criteria for reducing errors and consequently further improving SW quality. The author determined these success criteria in an extensive analysis, e.g. by thorough review of relevant literature, results of congresses on SW quality, interviews and considerable own professional experience.In the interviews with 18 experts in 3 countries, the determined success criteria were assessed regarding their importance, effectiveness and degree of networking. The results are shown in various figures and also explained.Other analyses of the success criteria will be / have already been published by the author on Amazon.com/.de.The assessment of the success criteria enables the reader and user of these criteria to set the right priorities for the optimization of SW quality during software development.Keywords: software, software development, software quality, error prevention, success criteria, importance of the success criteria, effectiveness of the success criteria, practical application.