For the first month or so I take a very humble listening position, even if I immediately see things I want to fix. More often then not, there is a background and a history to things that could lead to a) my “fix” being unnecessary and/or ill-informed and b) friction with the rest of the team because here comes a whippersnapper upending all our stuff. Process and code fixes are _much_ easier once you have good rapport…
I also always see contractors wanting to start self-initiated projects from scratch rather than working in the codebase, which is of course easier to produce a visible result in.