Whenever you are going to be in Court there are some basic rules you should follow. These rules apply in every Court regardless of whether you are going to be a witness or a party. The rules apply whether you are going to small claims court, traffic court, being a witness in divorce court or you are on trial for first degree murder.
First, always tell the truth. This isn't just some goody-two shoes comment – it's very important to tell the truth. Lies will be caught out in a flash and once you are seen to have lied about something, even a small thing, nothing you say will have much weight. Similarly do not exaggerate. If you are, for example, in pain three or four times a day, say so but don't say you are in constant pain.
Second, remember that Court is a formal environment. Speak respectfully to everyone in Court. Call the judge "Your Honour" (except in traffic court when the correct title is "Your Worship"). Call people by their formal names – use "Mr." and "Ms." Instead of first names. Also, remember the judge can see you the entire time you are in the courtroom so don't make faces or scowl or spend all your time on a smartphone or videogame unit.
Third, when called upon to speak take your time. There is no hurry. Speak clearly, loudly, slowly and be direct. Answer the questions asked and don't ramble on. Don't argue, just answer the question. Direct your words to the judge; he or she is the person who matters.
Fourth, dress properly. Do not wear a grubby teeshirt and jeans. It amazes me how often people come to criminal court looking just like criminals – if you want to be taken as a serious person worthy of consideration don't cover yourself in over the top jewelry and revealing clothes. Wear conservative, clean clothing in good repair. If you wear special clothes for religious reasons the Court will respect that and not require you take them off -- so a woman may, for example, wear her headscarf while testifying unless there is a very good reason to make her take it off. You do not need to wear expensive clothing, but you are in court. A guideline is to ask what a local High School teacher might wear to teach and dress at least as well as that. Show the proper respect and you will get respect.
Finally, and this is the hardest rule of all to follow, relax. The judge just wants to find out what happened. He or she is not interested in making you look foolish and will not allow anyone (including lawyers) to mock or humiliate you. Tell the truth and the rest will follow very naturally.