Arrive early or run the risk of the Court ruling against you without a hearing.
Not having proper witnesses to present documents.
Not having proper witnesses present to testify in support of estimates, reports, records, or other documents that the other person created. Evidence of costs actually paid can usually be testified to by the party presenting the evidence, but documents created by others stating an opinion of what something is worth or what their opinion is are usually subject to being excluded as hearsay.
Not having witnesses present to testify about what they saw or heard.
If your sister say it happen, your sister needs to be in court. Telling the judge "My sister is at work, but she told me X, Y and Z", is almost certainly not admissible.
Not having witnesses subpoenaed, especially third party witnesses and witnesses that are not family or friends.
Many a litigants have been told by a witness that the witness will be in court voluntarily. What happens if they do not show up? Many times a judge will not continue the case if the witness was not subpoenaed. When in doubt, subpoena the witness.
Thinking that the judge will only believe your version of events and not consider the other side's point of view.
Judge's are trained to listen to both side's of the case and then apply the law to their own opinion on the facts presented. The judge is required to give careful consideration to both parties. Just because you think your case is a the prettiest case ever, it does not mean the judge will share your opinion.
Not being prepared to go to trial immediately, whether moments after your appear in court or after the mediation (if the Court requires Mediation).
If you are given notice of a trial date, you will need to be ready to go the moment you walk in the door. Someone has to be first and it could be you. If the court requires mediation, many times the trial is held right after the mediation.
Thinking you will have time to hire a lawyer if mediation does not work out.
In some courts the notice of trial is also a notice of mediation. Usually both will occur on the same day and if the case is not resolved by mediation, the judge will usually want to move forward on the case. The case has usually been going on for several weeks or a few months and many judge's believe that is sufficient time to find a lawyer in advance.
Thinking the judge will automatically continue your case because you are not ready.
Judges are patient, but if a case is before them, they want to get it over with for the sake of both parties and the court. A request by the defense is regarded as more reasonable because they did not file the lawsuit. However, many time a request by the plaintiff is not due to the plaintiff deciding to file the action in the first place without hiring a lawyer.
Forgetting that time is money and that a settlement without hanging out at the courthouse all day has its own value.
If a pretrial settlement is offered, it is usually a good idea to factor in time and energy expended preparing for court, worrying about court, inconvenience for you and your witnesses and time actually sitting in the court house waiting your turn.
Forgetting that the Court's ruling could be worse than the other party's offer prior to trial or in mediation.
Just because you are asking for X amount does not mean the judge will agree with you. Many a judge has awarded only a percentage of a request and sometimes, nothing at all.