Do not be afraid to say "I do not know." If you do not know something, say so; do not try to fake it.
Take responsibility for your actions. If you are at fault, admit it and take the blame. If you are wrong, apologize.
Never gossip. Gossip can hurt the careers of two people: the person being talked about, and the person doing the talking.
Never say "That is not my job." Do not think you are above anything. Pitch in and set a good example, especially if the job is one that nobody else wants to do. Your willingness to do so will be noticed and appreciated!
Share the credit. People who share credit with others make a much better impression than those who take all the credit themselves.
Ask for help when you need it. Do not let a difficult task get out of hand. When you need help, ask for it -- before things get worse.
Keep your dislike to yourself. If you do not like someone, do not let it show. Never burn bridges or offend others as you move ahead in your career.
Do not hold grudges. Life is not always fair. If you were passed over for promotion, did not get the project you wanted, etc., let it go. Be gracious and diplomatic, focus on the future and move on. Harboring grudges will not advance your career.
Be humble. When you are right, do not gloat about it. Never say "I told you so!"
Make others feel important. Compliment others, emphasize their strengths and contributions, and help them whenever you can. They will enthusiasitcally help you in return.