Wireless Sensor Network (WSN) consists of very large number of sensor nodes which are deployed close to the area which is to be monitored so as to sense various environmental conditions. WSN is a data-driven network which produces large amount of data and also sensor nodes are energy-limited devices and their energy consumption is mainly associated with data routing. Therefore it is necessary to perform redundant data aggregation so as to save energy. In this work data aggregation is achieved with the help of two key approaches namely Clustering approach and In-network data aggregation. These two approaches help to save energy and thereby increasing the lifetime of the network. The proposed work has some key features like reliable cluster formation, high data aggregation rate, priority of packets, minimized overhead, multiple routes, reduced energy consumption which enhance the network lifetime. The performance evaluation of the proposed approach is carried out using Network Simulator- version 2.