The first month is the only time in a job when you are expected to know nothing, and it is the only time you will be forgiven for it. Spend it in listening mode: how decisions get made, what the team is proud of, where the last project went off the rails. Take notes; memory is not a filing system.
Resist the urge to propose changes. Every suggestion you make before you understand the history will be heard as a critique of someone's work. Ask questions instead: "How did this come to be?" gets you further than "This could be better." Curiosity builds trust faster than competence does.
By week five you will have earned the right to an opinion. When you offer one, frame it as a question — "What if we tried this?" — and offer to run the experiment yourself. The person who listens first and acts second is the one the team asks back for the next project.