The high penetration of television in Colombia and the fast deployment of Digital Television in the future, make necessary the study of the main characteristic: interactivity; thanks to which it is possible to have applications that allow viewers to be an active participant. Thus, it is important study the most adequate way to design usable applications for Interactive Digital television -- iDT. This paper presents a set of guidelines for designing applications in iDT environments, which have been generated from tests conducted at the iTD laboratory of the University of Cauca.