* politics: yes, they exist everywhere, but tend to be amplified at larger companies. polish your political skills, and one thing that I've learned is that it's important to "show, don't tell"
* fiefdoms: there are more of them, some more welcoming than others. be prepared for those that value power above all. you can't take it personally, or you'll go into a very dark place; "be the rubber duck", that is, stay floating no matter what and let the negative wash off of you like water off a duck
* duplication of effort: there likely will be tons of duplication of effort (even parallel projects doing the exact same thing), sometimes it's easy to work with others and come together for a common solution, sometimes it just plain won't happen (see fiefdoms). no real advices here, just that you need to be aware
* technology stacks: sometimes some groups will be stuck with what seem to be very old technology stacks, or things that don't seem to make any sense. look at the group you'd be joining and who they interact with, find out about the pain points before you join so you aren't surprised. even a small change can affect a lot of people at that scale, so approach changes and modernization gingerly.