Start top down: ask what has the most business value and take care of that first. You will not be able to do everything an experienced sysadmin will do, so you

Start top down: ask what has the most business value and take care of that first. You will not be able to do everything an experienced sysadmin will do, so you need to prioritize to the extreme. Only deal with important stuff. The most technical aspect: don't lose or destroy the data! Downtime is fine, losing data is catastrophic. Grow a thick skin or move on. You will be the target of complaints. A lot.