A new job can be just a little bit scary. Even if you've worked in the same field as your new job, that doesn't mean that this company does things the same way. Even if you're working for the same company and have been promoted, it's still a new job with new responsibilities, and that can be stressful. When you start a new job, no matter how you acquired it, what it is, or how much experience you have, you want to make a good impression. Be polite but don't be overly friendly and start telling people your life story.
They don't know you well enough for that, and most of them probably don't care that much. It could also be perceived as either bragging or looking for sympathy depending on your circumstances, and people don't usually respond well to that. Keep yourself to yourself without being rude, at least until you get to know these people better. If they are your subordinates, you don't want to be too friendly with them anyway, because it often leads them to think that they are your 'buddies' and can get away with anything. Employees and bosses really can't be friends.
When you arrive for that new job, make sure to be on time and to dress appropriately. If you aren't sure about the dress code, ask before you arrive for your first day. The interview during which you were hired is a great time to inquire about things like dress codes and working hours. A new job might make you nervous, but try not to show that. You should appear confident so that your employer feels that he or she made the right choice in hiring you.
If you don't know something, ask, and listen to what others have to say. It's not a wise idea to act as though you know everything, even if what you're being told is redundant and you already understand it. Your new employer must make sure that he or she fulfils duties and obligations for hiring new employees or promoting them and making sure they understand the job. Just relax and be willing to learn, and you'll have less stress at your new job.