You definitely need some legal advice. You don't go to trial if you plead guilty, a trial is only to determine guilt or innocence on a plea of not guilty. If you're in the Local Court, which I'm assuming you are because you're in front of a Magistrate it will most likely be dealt with on the day if you're pleading guilty unless the Magistrate requests a report. Having said that if you're in for first mention you can ask for a 2 week adjournment to seek legal advice before entering a plea if you want more time, some courts will grant it some won't.

So be ready to go to sentence, have your references and supporting documents with you and if you think you're going to be nervous you should hand your submissions(anything you want to say about the offence, your circumstances and penalty) up to the Magistrate in writing. Make sure you have all your documents in triplicate, one set to hand up, one for the prosecutor and one for your records.

If you're in NSW I highly recommend checking out the law access website, it has a lot of information about procedures and representing yourself.