What is the most important rule of a treasurer?

What is a guideline you follow that has helped you stay accurate and organized? When you start a new job, what is the first priority? Learning systems and understanding the current financial status of the company will set you up to be knowledgeable and prepared. Once you're in the position, staying up to date on the financials and being a resource in order to provide sound information to back up decisions are top priority. If you know of a rule that will help you be successful, share it!