Like any other quality attribute, usability imposes specific constraints on software components. Features that raise the software system's usability have to be considered from the earliest development stages. But, discovering and documenting usability features is likely to be beyond the usability knowledge of most requirements engineers, developers, and users. We propose an approach based on developing specific guidelines that capitalize upon key elements recurrently intervening in the usability features elicitation and specification process. The use of these guidelines provides requirements analysts with a knowledge repository. They can use this repository to ask the right questions and capture precise usability requirements information.