Hi Wendy A Anderson,
If you have no criminal record, ask the police to recommend you on the
diversion program. I know that careless driving offences can be diverted onto the program. Essentially, a diversion program means that you agree with the police to undergo some conditions (e.g. partake in a driving course, write an apology to the police/council) and in exchange, the police drops all charges against you for careless driving. Because the police drops the charges, you will not get a conviction and you will not be asked to enter a plea. You will likely need to admit your responsibility with the police informally (to show remorse and that you understand you were wrong). Because you will not have a conviction, this incident will not be recorded on your criminal record and your criminal record will be kept clean.
You can request it, as this is your first offence and careless driving is still relatively minor. Both the police and the Registrar of the Magistrates' Court will need to agree to it. This may mean, you will need to go to court for an informal interview with the Registrar for them to sign off on it.
If the police decide to press ahead with the charge, and you believe you did drive carelessly (e.g. the car hit something), then pleading guilty will likely mitigate your sentence because it shows you've owned up to the responsibility, you show remorse and you have saved the court and police a lot of time and resources. However, you should only plead guilty if you honestly believe you were guilty and feel you wish to plead guilty. It is completely up to you.