Existing EU directives and national laws on the reuse of Public Sector Information have motivated the creation of a large set of open data portals across Europe (following a global worldwide trend towards openness in the publication of open data). This is also the case in Spain, where the national government and national agencies, as well as regional governments and institutions, and local city councils, have started publishing actively open data in their corresponding portals. However, this wealth of data has been generated in a bottom up fashion, what means that the selection of the datasets to be published is done by those publishers independently, and that the formats and data structures in which such datasets are available are generally very heterogeneous. This generates problems for those companies and individuals who want to reuse such data across several institutions. This tutorial will present the work that has been done in the context of one of the Spanish normalization working groups towards the definition of an open data maturity model for cities and for the selection of a set of ten datasets to be published by cities, and which is now being extended to handle many more datasets. The goal of this tutorial is to show how this process could also be applied in other countries and by other cities in different parts of the world.