The workplace can be a tumultuous place, but it is always possible to stay professional. Things might be turning upside-down around you, but it is imperative that you maintain your composure. Being professional is the best way establish a concrete reputation. It just may save your job someday.
Wardrobe: This goes without saying - you have to dress the part of the professional to be a professional. No one has ever advanced at work or preserved their job by dressing like a slob. There is no advantage to dressing in an unflattering way. Humans are primarily visual creatures so you have to appeal to this faculty as much as possible. Wearing decent clothes is easy, just do it. It just might save your or boost your reputation. It is the ultimate professional accessory.
Emotion: Excessive emotion in the workplace is counterproductive. Usually "big" events blow over, unless you make them into "bigger" events. Just fix the problem and move on. No crying, griping, or screaming. Just fix it.
People appreciate other people who solve problems and take steps to prevent problems from happening.
Communication: Always use politeness and be courteous to everyone (at least to their face). It's counterproductive to be combative and non-cooperative. Try not to become excessively animated. People surround people who present a calm demeanor and a smooth, confident communication style.
Punctuality: This encompasses not only being on time, etc., but also organization. Nothing is more unprofessional than a person who is extremely messy. Nothing is more unprofessional than when someone is always late or absent.
Relationships: Professionals associate themselves with the top performers at the company. The people you surround yourself with reflects that type of person you are. Also, forge a bond with your supervisors and bosses. They are your best ally in the company, so make sure to develop these relationships.
Appropriateness: My boss shared this insight with me - a lot of professional life is dictated by appropriateness. By "doing the right thing" even if that means "hurting" yourself in the short term, you are establishing an honest, hard-working, rock-solid reputation. Reputation is everything.
Loosen up for certain occasions, but always be acutely aware of yourself. A bad showing at the Christmas party can be devastating to your image.