In 2011 we published a paper showing that people update their beliefs to a greater extent in response to good news (e.g., learning that the likelihood of robbery is lower than expected) than bad news (e.g., learning it is lower than expected) (Sharot et al., 2011). This phenomenon, which can lead to increased optimistic beliefs, is absent in depression. Since then, our belief update task has been used by many others to test a wide range of questions related to belief formation and optimism. Most of these studies are rigorous and well conducted. However, a small number of researchers have used the task inappropriately, inserting new confounds and failing to control for other potential ones. This has resulted in the report of false findings which have muddied the literature and caused confusion. Given these incidents and the enthusiasm for using the task across different disciplines, the need for guidelines on how to use the belief update task correctly has become apparent. The belief update task can be a helpful tool in studying beliefs in domains ranging from climate change to health, but like any other task it must be used properly if valid conclusions are to be reached. We hope this guide will be helpful for scientists who would like to use the belief update task, as well as readers, reviewers and editors who are required to evaluate studies using this task.