I’ve moved teams in Microsoft many times and discovered it’s very important to ‘land’ well in your new team. First impressions usually stick around for awhile! Here are the basics that helped me land well in a new team (and new project). A good way to think about this mail is a ‘bag of ideas’ and you can lift whatever you think might be helpful/useful and toss the rest. 
Things to remember
- This change is likely as disruptive for the team as it is for you, and resets the team back to the “forming” stage of group dynamics. You should go the extra mile in trying to make others comfortable working with you.
- It’s totally OK that you don’t understand the big picture, it’s not necessary (yet) to have everything understood before you have an impact.
- Be creative in leveraging your prior experiences, even if they don’t map 1-to-1. You’ve learned a lot already, don’t hesitate to use it! The worse that can happen is that it doesn’t apply and we move on.
The top 3 things to do ASAP
Meet the Team: You’re now with a new group of folks who you likely don’t know, but also will be working with for a long time. Go meet everyone! If you’re more junior on the team, go meet every senior person, if you’re more senior, go meet every leader on the team. Introduce yourself, but also ask a question – “what’s your favorite feature?”, “Why do you like the team?”, “What’s your area of expertise?”, “What should I focus on first?”, “what’s the biggest thing holding the team back?”, “what’s our biggest challenge coming up?”, etc. It doesn’t matter (much) the question, just pick one to get them talking, you’ll have a much better impression of people beyond the 2-second introduction.
Over-communicate: There’s a lot of things happening around you that you don’t understand. Status meetings, manager updates, hallway scrums, etc., and be honest – you don’t understand the rhythm of this team yet. Totally fine! You should definitely over communicate with your manager and peers at least until you understand (or your manager helps you understand) the right time/place for each type of message. Status reports are great, but you can take this a step further and write down what you believe the expectations are of you (IE: update your commitments/goals!), make it clear if you won’t be on time with any tasks and why, etc. You are earning a reputation during the early phase after you join a team, you should strive for dependable and trustworthy and over-communicating in the early stages helps with this.
Make an impact: Find something to go have an immediate positive impact on the team. Great candidates for this are small-ish and somewhat isolated tasks that you can complete quickly and move on. It could be as simple as helping out one of your new peers with setting up machines, jumping in on exploratory testing/bug bashes, trying out some customer scenarios or unusual configurations, write a tool to simplify some part of the new team’s processes, etc. The goal in this is picking something that you can complete and move on. This helps establish a pattern of results as well as being motivating to go after the next (hopefully bigger) items.
Hope this helped! If you have other things that helped, let me know in the comments below!