The implementation of an ERP (Enterprise Resource Planning) demands the development of a complex project. On one hand, the scientific literature presents some key factors which allow the project to reach the expected objectives. However, these researches do not consider the dynamic relationships that take place among these key factors, although interrelations can benefit or stop the project development. On the other hand, there are different useful strategies for an ERP implementation that directly affect the project development. This paper develops a generic model to identify the relationships among the main key factors (best fit with current business process, resistance to change and training). The model has been validated by a company dedicated to ERP implementation in Spain. Finally, the model will also be useful to analyze the impact of the different strategies in the management of an ERP implementation project according with the project cost study.