Just joined a new team as a senior dev last fall and went through this. I simply worked my ass off the first couple of months and asked a lot of questions and banged out some very high quality initial commits to make a strong first impression. Have a zen mind/open mind, things will be different and you may not care for some of the approaches taken. Play the long game and gradually make suggestions and changes as you get to know the landscape. My initial feedback from management was very positive, so this approach worked for me.