Cleaning, organizing, and documentation are high priorities.

Every job I've worked at has had mountains of "The last guy didn't..." that you walk into and it's always a huge pain in the ass. They didn't throw out useless things, they didn't bother consolidating storage rooms, and they never wrote down any of their processes, procedures, or rationals. I've spent many hours at each job just detangling messes because the other person was to busy or thought it unimportant and didn't bother to spend the time.

Make it a priority, allocate the time, and think long-term.