Eliciting requirements is well known to be a difficult task. Several strategies exist that makes it possible to elicit information from different information sources. These strategies vary and should be selected in accordance with the situation at hand. For instance, selecting a strategy to a situation where there are available COTS solutions is different from a tailored and specialized software application. This article reports on a strategy to be used before the selection of an elicitation strategy. We are concerned in how to select the information sources that should be taken in consideration for the requirements elicitation. We consider this activity of fundamental importance to the elicitation process. Selecting the appropriate sources is fundamental as to deliver quality requirements. The article describes the proposed strategy and exemplifies it with a well known and published case, The London Ambulance Service.