You should typically devote the first block of 30 days to learning and building personal credibility. Like Michael, you should negotiate for this early learning period and then try to hold your boss to that agreement. Then you can proceed to develop a learning agenda and learning plan for yourself. Set weekly goals for yourself, and establish a personal discipline of weekly evaluation and planning. Your key outputs at the end of the first 30 days will be a diagnosis of the situation, an identification of key priorities, and a plan for how you will spend the next 30 days.