Developers write logging statements to generate logs and record system execution behaviors. Such logs are widely used for a variety of tasks, such as debugging, testing, program comprehension, and performance analysis. However, there exists no practical guidelines on how to write logging statements; hence, making the logging decision a very challenging task. There are two main challenges that developers are facing while making logging decisions: 1) Difficult to accurately and succinctly record execution behaviors; and 2) Hard to decide where to write logging statements. This thesis proposes a series of approaches to address the problems and help developers make logging decisions in two aspects: assist in making decisions on logging contents and on logging locations. Through case studies on large-scale open source and commercial systems, we anticipate that our study will provide useful suggestions and supports to developers for writing better logging statements.