Time synchronization is an important issue in wireless sensor networks. Many applications based on these WSNs assume local clocks at each sensor node that need to be synchronized to a common notion of time. Some intrinsic properties of sensor networks such as limited resources of energy, storage, computation, and bandwidth, combined with potentially high density of nodes make traditional synchronization methods unsuitable for these networks. Hence there has been an increasing research focus on designing synchronization schemes. This paper contains a survey, relative study and analysis of existing clock synchronization protocols for wireless sensor networks, based on a various factors that include precision, accuracy, cost, and complexity. The design considerations presented in this paper will help the designer in structuring a successful clock synchronization system. Specifically, the comparisons presented based on various factors will provide basic guidelines to the designer in integrating various solution features to create an efficient clock synchronization scheme for the application.