* Things move slowly.
* You need to be able to play the game if you're going to move up, if you want to stay in the same role don't make waves.
* Other people are playing the game. Sometimes if you're trying to make changes, even if they're going to be beneficial, you are going to run into people who have a vested interest in you not improving things. Don't let it get you down, pick your battles.
* You are way easier to replace than you think you are, don't start fights with people that can let you go. Most won't hesitate to remove you if you make their life difficult.
* Make the most of the perks and don't bust a gut, if anyone notices it'll be because you're making them look bad. Going above and beyond will earn you a pat on the head but nothing more.
* People will be doing everything they can to cover their own ass, don't let them use you for cover.
* Don't get too attached to projects, things get killed or mothballed. Years of work can just be binned without much warning. Make sure you're not defining yourself by what you're doing at work.
I've done my time at a couple of big firms and had people working with me on teams that want to be a 'craftsman' or don't really understand these workplaces, the thing I tell them to remember was "don't fight the waves, just let it wash over you". You can't win, you'll just knacker yourself out and drown.
Don't feel bad if you hate it or want to leave, it's not for everyone. Also don't feel bad if you love it, plenty of people have much better things going on in their life than work and are happy to coast along at a big firm doing what needs to be done.