Take time to learn how to use your company's issue tracking and source control systems and
how they are used. For example, the place I work now is very opinionated about squashing and rebasing. Something I am personally not keen on, but that is their "way".
Always take small bites at a time. Don't do huge changes or drive by refactoring in the context of a commit.
Do not be shy about asking for clarification or help.
Resist pride of ownership. Try to separate a review of your work from a criticism of you.
Your new employer has traditionally done stuff "their way". Try to integrate into it and understand why they do it that way BEFORE your try to champion changing the way they do it.
All offices have politics. Make sure you understand them before you complain about how crappy one particular person is.
Understand how you will be evaluated and make sure you are working in that light.
Dress for your boss's job
Be the first to arrive for meetings. Make sure you give everyone a chance to speak.
