The only things I'd add to all the above is communication and networking which link together.

Communication between you and your new boss(es) is important so you can build a rapport and feel at ease with each other.  Particularly in the early days you need to give 2 way feedback to how you are going to work/change ways of working.

Communication and networking within the company and outside is also key - talking/meeting with other people that you deal with regularly/the people that your boss deals with regularly.  When you build up a rapport it is easier to approach people for help/contacts for information etc.  You will also probably be approached as the font of all knowledge so keeping a note of useful information/people is handy.