The need to address behavior surprises many law students and young lawyers because they carry the assumption that adults should and will behave in a professional manner. Unfortunately, experience shows that assumption is far from reality. Being a professional goes beyond your work product and your everyday work practices. It is critical to a successful and respected career that lawyers learn and maintain professional behavior.
Others liking and/or respecting you will make your life easier. Those who like you will be more willing to give you the honest truth you need to hear or be patient with your faults. While being considered a professional may not make your career, a reputation as unprofessional can destroy it.
Professionalism is not a guarantee; you have to work for it every day. One mistake can cause you years of trouble and undo years of clean practice. At the end of the day, people will gossip, do not give them a reason to gossip about you.
Be on time, even if that means being early. While this is included above in relation to organization, it is important enough to include again. Being on time is one of the most tangible means of expressing professional behavior. Promptness may not always be remembered, but tardiness will be. Learn your own behaviors, traffic patterns, as well as, meetings and appointments that are likely to run long and plan ahead for those circumstances. In parallel, respect the time of those people you are dealing with, be it a client, judge, attorney, or jury. Economize your language and arguments to respect that others lead busy lives. Once you make your point, stop talking. The fact that a court or board has given you time to speak does not mean you have to use all of it.
Because the legal profession is so often adversarial the need to respect those you interact with is often lost. However, being generally polite and respectful of your colleagues, clients, opponents, and decision makers, is a key component of maintaining professional behavior. Get along with the opposition; judges and clients hate lawyers wasting time over petty issues. Respect for others also includes remembering to alter your behavior to the circumstances you are presented with. While you may have a collegial relationship with a judge, a joking repertoire may not be appropriate in a court proceeding. Learn who you can joke with and who you cannot.
Similarly, never yell at a judge even if you think you are in the right or just inserting yourself into a conversation. While clerking for the U.S. District Court of Delaware I saw multiple attorneys interrupt and at times yell at a judge. Regardless of the content of the interruption, it never worked to benefit the attorney or their client. This went so far as to once see an attorney explain to a Federal Judge, how things are handled in Federal Court. It should go without saying that the first conversation in chambers was not about the merits of the arguments, but about the lack of professionalism of the attorney.
It’s not about you
A personality trait I have seen in many attorneys is a desire for the spot light. While the ability to work a crowd and engage with everyone is valuable, many forget that they are working for their client’s best interests and not their own personal acclaim. Do not place your desire for attention or your ego above the best interests of your clients.  I once witnessed at attorney sabotage his argument by explaining that the flaw of his presentation could not actually be a flaw, because as a law professor he was simply too smart to have missed an issue. That attorney’s ego cost his client an argument and him the respect of the court.
In contrast, introverts, myself included, are also well represented in the legal profession. As an introvert, I must work in the opposite manner to make sure that my natural reservedness does not harm my client.
Pick your battles
In almost every project you encounter, whether it is a case, a negotiation, or any other interaction, you are likely to have a number of disputes and issues that require resolution. Learn to distinguish the battles that must be fought to properly represent your client from those issues that are inconsequential. While there may be points in dispute that are not critical to your client but remain valuable trading pieces in a negotiation, there are battles that are simply not worth fighting. Fighting meaningless battles can make you appear petty and even unprepared. When you have lost a point, accept it and move on. Stipulate to facts and law where possible to save wear and tear on your audience. I once witnessed a trial derailed for half a day because one side refused to accept a piece of evidence because the picture in question had a ruler included that was not initially noticed. While technically in the right, the disputing party agreed that the picture was accurate, the ruler was accurate, and that no harm would come from the presentation. At the end of the day, the disputing party won the argument, but cost themselves significant capital with the court and their opposition without changing the impact of anything the jury would see.
The manner in which you physically present yourself will color how you are perceived. Dress professionally, but not eccentrically. While a monochromatic, neon pink shirt and tie combo may technically meet professional standards, it draws the attention away from your arguments to your fashion sense. Gentlemen, take your keys and phone out of your suit pockets, they make you look lumpy and unprofessional. The importance of physical presentation should carry to your client and those associated with you. While attorneys rarely show up in an NFL jersey, I have seen clients appear in court in jerseys, t-shirts, and pot-leaf sweatshirts. Make sure your clients and your support staff know how to come across professionally.
In the same context, carry yourself in a professional manner as you sit, stand, and speak. You are not on your couch and you are not at a funeral, find the right balance. Be aware of your volume, in both directions. While volume may be occasionally useful to make a point, constantly yelling will give your audience a headache and whispering will drive them crazy.
Get to know your personality
Lawyers come with many different personalities, and while they can all lead to a successful career, it is important to learn your strengths and weaknesses. An introvert, like myself, may never be a social butterfly, but can learn to engage with others and develop valuable relationships. Once you know your strengths and weaknesses, improve yourself. Learn to rein yourself in if you have an overwhelming personality or how to embrace social settings if you are reserved. Be charismatic, but in the context of your personality. And, at the end of the day, do not be a jerk.
Know your technology
When you will be using technology in a court room, board meeting, or other interaction, learn how it works before you need it. I am no longer surprised when I attend a hearing or board meeting and witness an annoyed judge or council member watch an attorney fumble through starting a projector or computer system. Practice ahead of time.
Lawyers are not better than non-lawyers
Lawyers have a level of education that non-lawyers do not have, do not mistake that educational disparity for a disparity of intellect or ability. Work with non-lawyers and understand that you do not have their specific knowledge, whether they are electrical engineers, chefs, mechanics, or any other profession. If you fail to recognize this, you are likely to alienate your audience or client. Juries, clients, and decision makers do not look favorably on attorneys they think are jerks. Be kind to the non-lawyers, whether secretaries, support staff, court staff/reporters, or anyone else, in your work life. Those people can help you or make your life hell; take the time to make sure they are in your corner. Those people also are friends and colleagues with decisions makers and people that impact your life, and they talk to each other.