The goal of this work is to contribute to the improvement of the generic development process in product lines engineering, i.e. for software product families. The work integrates the best (in the opinion of the author) parts of the given state-of-the-art, and contributes some new aspects to the process. Some aspects of this presentation include topics like variability modeling, handling variability and feature modeling, especially extending feature models with feature weights and fuzzy description for variable features. For modeling requirements the use of a specialized feature model for modeling features in UML is exemplified in the e-Commerce domain. Another contribution is the proposal of modeling flexibility with feature models as shown in an example of Web services and the introduction of a version-based approach for feature models. All suggested new capabilities and methods are integrated to provide an improved framework for the development of product families. For the fulfillment of the generic system architecture the generative techniques like frame technology are recommended. This supports reuse in the evolution and maintenance phases of system family members.