Wireless sensor networks have a wide range of applications and can be used for various purposes in different environments. Wireless sensors are small and they are mostly using battery supplies. Communication, sensing and computing have the most influence on performance and power consumption of wireless sensor networks. In this paper we describe layered architecture of wireless sensor network protocol stack and discuss the advantages of cross-layer approach. The articles that are using a cross-layer approach for improving performances and energy preservation in wireless sensor networks are reviewed and state of the art is presented. One of the fundamental problems for wireless sensor networks is how to systematically make a performance evaluation. Because there are plenty of different wireless sensor network optimization methods there should be a universal benchmark suite. We have proposed some useful guidelines for its development.