The aim of this paper is to present an innovative approach for optimal placement of piezoelectric patches in the context of vibration control or energy harvesting applications. Targeting a specific mode shape and assuming that the addition of thin surface-bonded piezoelectric layers has a sufficiently weak influence, the analysis of the stress or strain fields over the bare structure directly provides the best areas for maximized piezoelectric coupling. The area extension of a patch is then optimized based on the modal electromechanical coupling factor. The whole process only requires a standard finite element model, without the need of any piezoelectric elements. Three criteria of increasing complexity are proposed and numerically validated on a benchmark structure which offers a non-standard geometry. Such criteria and methods may have a strong interest in an industrial context where coupled models or specific expertise in piezoelectric coupling are not always available.