Think back to how you felt the first day at a new school, then fast-forward 15 years. You're still being regarded as the new kid, just in an office setting and by other adults instead of grade-school classmates. Smile, be confident but not cocky, and be friendly but not overly so. Just as your new colleagues are checking you out, you need to listen to and observe them. Ask a few well-placed, educated questions that signal your commitment to becoming a contributing member of the group as quickly as possible. And try to learn one or two key things about each of your new colleagues to signal your interest in them as individuals.
From the first moment you walk through the front door, carry yourself professionally. Greet people with a firm handshake and a smile on your face. Remain courteous and respectful, but avoid trying to get too friendly, too fast: your new colleagues might think you're trying too hard. Steer clear of jokes, potentially controversial subjects and profanity, even if your new colleagues appear to have a very relaxed style around the office. Never badmouth a former boss, co-worker or job situation.
Look and Listen
Carefully observe your new co-workers to get a sense of the overall office culture. Watch the way they interact with one another and with the boss. Make mental notes about which employees hang around with each other, as well as any obvious animosities. Follow co-workers' cues about lunch hours, cubicle chit-chat and leaving for the day. Look at how everyone is dressed to get a sense of what's appropriate and acceptable in the office -- for example, do your male co-workers leave their jackets on all day or are rolled-up shirt sleeves the norm?
Show your interest in both the professional aspects of the new job and in your new co-workers as individuals. As you are meeting people, take note of which ones seem to be well-connected within the office, according to Katharine Hansen of Quintessential Careers, and incorporate these people into your professional network. These are the people who will likely offer the most insightful information about how things really work in your new organization. Ask them specific questions about policies, processes and preferred communication styles. With all your new co-workers, avoid asking personality-specific questions; for now, observe the boss's behavior to make your own determination about his style.
Get to Work
Show up on time and put in a full day's work from the first day, even if you don't yet have much in the way of specific assignments. You need to walk the fine line of contributing to the work effort without stepping on toes or being critical of how things are done. Begin learning your job duties and responsibilities right away, and offer to help with ongoing projects or assignments to show your new co-workers you are a team player. Ask your new boss what she wants you to start working on, then do it.