1. You’ll probably be overwhelmed by all the new information, but don't freak out about it. In my experience, you can only retain one-third to one-half of the information that's thrown at you during your first day on a job. This is normal. Eventually it’ll all make sense.
2. Listen more than you talk. The first week is about you assembling a framework of understanding for how your new company works. Hold off on suggesting changes until you get to know the environment and employees and how and why they do things.
3. Know that some managers are better at training people than others. If your manager seems haphazard in her approach, don't be shy about asking for what you need. It’s fine to ask things like: "What things should I be focusing on this first week?" Or, "What can I read to get a better understanding of ___?" Or, "Are there samples of how this has been done in the past that I can look at?"
4. Find out what your manager wants you to accomplish in your first month. What are the big projects you should be focusing on immediately, and what can wait?
5. Pay attention to the culture. Observe how others act and you'll absorb a ton of information about cultural expectations. Are people compulsively on time for meetings? Do they take a real lunch or eat at their desks? What hours do most people work? Is there a lot of chitchat during the day, or do people stay focused on their work? Do people primarily use email to communicate or talk in person?
6. Don’t get drawn into office politics. Eventually you might not have a choice, but until you have the lay of the land (which generally takes months), don’t risk being associated with the office complainers or gossips. Stay positive, don’t solicit gossip, and be nice to everyone.
7. Don't turn down offers of help. Even if you don’t think you need the help, accept assistance anyway. If nothing else, you'll begin forming bonds, but you'll also probably gain useful information. Keep in mind that you don't know what you might not know!