Wireless Sensor Networks, consisting of sensing devices which sense the environment and communicate information among each other, is an emergent field in wireless networking with many potential applications. Efficiency of energy consumption is an important objective in these wireless sensor networks. All these sensor nodes have limited battery supplies and limited sensing capabilities. Network Lifetime of wireless sensor networks has a strong dependence on sensors' battery power. Since these sensor networks have large numbers of nodes, allowing some nodes to sleep for particular intervals of time can result in an increase of network lifetime. In this paper, a sleep scheduling heuristic called the Grid Scan heuristic is proposed and implemented. The method extends network lifetime significantly by scheduling sensors such that it maintains a threshold level of coverage. Scheduling sensors to sleep state and active state intelligently extends network lifetime significantly. The Grid Scan Heuristic intelligently decides when a sensor should be turned on and off such that the wireless network maintains a level of coverage. The performance of the Grid Scan approach is compared with another sleep scheduling algorithm called Randomized Scheduling, which is an already existing algorithm in the literature.