What are the biggest do's and dont's when starting a new job?

(1) Listen at least as much as you speak--you need to learn quickly. (2) build an Execution Plan for the first 90 days; (3) have supervisor validate and/or re-prioritize items on your 90 Plan; (4) Make it a point to get to know at least 1 new person a day; (5) assume nothing! Ask.

Do: Arrive early and stay late. Check your messages promptly. Say yes enthusiastically to whatever you are asked to do. Get your projects done accurately, thoroughly, and on time. If you don't know how to do something, figure it out or get expert help. Be courteous and pleasant to everyone. If you're supposed to generate your own projects, be proactive. Be a contributor. Be someone they are glad they hired.

All of the above is good advice. Trying to deliver a little more than is expected of you is always a good practice. I'd also add that you should find out about the politics of your new organization, while remaining above the fray where office gossip is concerned. This is not an easy thing to do, but every organization has its power brokers, cliques, workers, slackers, and troublemakers. Knowing which people to align yourself with and which to avoid will be an important component of your success in that company. Keen observation, while keeping silent about it all yourself, is essential to determining this.

Don't chit chat all day.
Do understand the Job Description, study this as this is the evaluation of performance.
Don't assume. Have a full understanding of the goal or ask questions during process.
Do be pleasant and geniunely interested in the position and the people around you.

In addition to those already mentioned, stay neutral and don't get yourself in cliques - don't get labeled. Also, reserve your comments/judgement/opinion of others and in like manner, don't get involved in conversations about other managers esp your supervisor. A good response when someone is trying to get you to comment on someone is to say - 'hmmm' or 'interesting perspective'.

It really depends on your role and the situation surrounding your hire.
If are you in a leadership role?
Get to know those who report directly to you. What are they struggling with? What systems are in place that work well?
Get to know your internal supplier and customers. Build relationships. Reach out. Share and be open. People want to know the real you.
If you are in a leadership role and you have been given a specific goal or agenda
Gather your team and share your background
Discuss what is important to you and what makes it significant/important
Have each of them share a bit about themselves, their experience, their concerns.
Talk about how your expectations
If you are going to change things, be sure to share what won't change and how they will be involved.
If you are in a non-leadership role
Display curiosity and enthusiasm
Learn procedures, ask questions, determine your job's objectives
Build relationships, learn who to go to when you have questions or need help
Be flexible, be friendly and sociable, stay focused

Don'ts
Don't complain about your old job, old boss, old colleagues
Don't believe all the rumors and stories you'll hear about people and events
Don't get too frustrated as you attempt to learn new methods. We are all beginners at some point.
Don't forget to read whatever written material you are given so you understand the "rules".
Don't fear asking questions

The Starting Days are crucial for success. Long-lasting
impressions are made during this time, and early decisions often become our trademark, affecting how others view us.

Don’t think because you are new, you can sit back and take it easy for a while and let everyone else show you what to do. Show initiative and enthusiasm.

Don’t waste the honeymoon period,you need to start familiarizing yourself with the organization immediately
and settling into your role.

Don’t try and re-invent the wheel from day one. Learn the job and the processes that are in place before you start trying to change them.

Don’t be drawn into discussions about other members of staff. You don’t know whom you can trust and whom you can’t at this stage. Stay away from office politics.

Don’t use your work phone to make personal calls without asking and even then, keep them to a minimum.

Don’t leave on the dot, come back late from your lunch breaks or start booking holidays straight away.

Don’t sit in silence and wait for people to talk to you. Think of questions to ask people and start conversations yourself.

Do
Demonstrate that you have researched the company & products wherever possible. Have a note book and pen ready and write everything down.

Ask questions when you don’t understand (you are not expected to understand everything).

Make sure you are well presented and that your body language indicates enthusiasm and willingness to work.

Look sharp and smile—show warmth,your personal grooming and your facial expressions send stro ng signals when others first meet you. A smile or a friendly greeting to others often seals their support as you start a job.

Try to remember people’s names. It makes your life easier

In addition to all above, manage expectations. Don't over-promise.

An interesting question especially since several of us were discussing this topic earlier today. My big problem with new talent is that frequently they want to change the world in the first week. Sometimes it seems just to put their stamp on the organization. I've always believed one needs to observe and analyze before making any changes. Understand the organization and the people. See where real improvements can be made not just change for the sake of change. Evolution not revolution.

I have a short answer for this one. I may revisit later. However the first things that come to mind right now are:

DO: Be yourself. DON'T: Let it all hang out.

DO: Hit the ground running and add value. DON'T: Overextend yourself and give an impression of your capabilities to others that you will not be able to sustain in the days to come.

Be a 100% there, and do your best for no other reason than its right. You can only do your best, research backs this up, if you are always striving for improved skill.

Results and recognition always take care of themselves. People will notice superior attitude and work habits.

A new job is a fresh start and the only opportunity you have to create a first impression. Make the most of this opportunity by starting as you intend to continue - dress well, turn up on time, be enthusiastic, listen, ask lots of questions and try to get to know people. Be proactive - e.g. ask people if you can organise a short meeting to find out what they do and how it might impact on your role (even if you aren't in a leadership role). Don't assume the position description is accurate or that everything in it has equal importance. Ask your boss what the priorities are and what you have to do to succeed in the role. Ask what you'll be judged on at the end of your probationary period.

Don't criticise either your old organsation or how things are done in your new organisation. What until you learn the context and develop trust before making a few suggestions. There may be a good reason why it is being done the way it is being done even if it doesn't seem best practice to you initially. And don't start every sentence with "at XYZ we did it this way" as it does get annoying.

If it is a leadership role then align yourself with people at the same level as you, familiarise yourself with strategies and operational plans, ask for the personnel files of those reporting to you and arrange meetings with each of them and be a leader from day 1.

Understand the job and role you were hired for. Scan your environment and know who the players are. It is important to be ethusiatic and a go-getter when starting a new job. Stay above (away from) the politics and gossip....atleast for the first 90 days....until you know who you are working for and with!!

You have some great answers here, as a person that used to switch jobs/companies often, I've learned that you have to be yourself and make sure that you treat others the way you want to be treated. If you smile and say "Good Morning" others will greet you that way and can make you feel like a part of the team faster. Keep in mind that yo are only one person and haven't gotten into the rumor mill yet, and the information about you will travel fast.

This does not matter your posistion, even the CEO needs to be sincere so people will want to approach them even for water cooler chats, which can be more valuable than some scheduled meetings.

Then you need to learn the culture of the company, so that you don't stab yourself in the foot or short-change your career before you know it.

This answer, for me truly defines what makes a good employee: being 100% there. It doesn't matter how early you arrive or how late you stay, or how nice you act if you aren't really there.