The only way to continue a trial in California is by motion or ex parte application.
A motion is brought on 16 court days notice, while an ex parte application can be brought on as litle as 24 hours notice.
Whether brought by motion or ex parte application, the standard for obtaining a continunace of a trial date are the same.
The Grounds for Continuing the Trial Date
California Rule of Court 3.1332 provides that the trial date can be continued on motion or ex parte application on numerous grounds including that a party has been unable to obtain "essential testimony, documents, or other material despite reasonable diligent efforts", or there has been a "significant unanticipated change in the status of the case as a result of which the case is not ready for trial".
In ruling on the application, the court should consider, among other things, the proximity of the trial date, whether there have been other continuances, whether all parties have stipulated to a continuance, and whether the interests of justice would be served by a continuance.
Arguments to Make In Support of a Continuance
Some good arguments for continuing the trial date are that the other side has failed to provide requested documents or interrogatory responses, or has failed to appear for deposition.
Another good ground is unavailability of counsel due to injury, ilness, or trial conflicts.
Finally, counsel can argue that there has been a "significant unanticipated change in the status of the case as a result of which the case is not ready for trial". This can include a newly discovered witness, document, or other evidence, especially when presented by the other side.
Trial continunaces are difficult to obtain. As such, a party should always assume the case will go to trial on the date it is set, and should never count on a continunace being granted.
However, if a continuance is reasonable, and in the interests of justice, judges will sometimes grant them. However, prudent counsel will never count on a continuance, and should always be prepared to try a case on the date set for trial.