A credit score is a snapshot of how you have handled credit in the past. Lenders may look at it, along with your income and expenses, when they assess an application. It is not a moral grade, and it is not the only thing they consider, but it can influence whether an offer is made and on what terms.
What usually helps
Paying existing accounts on time is the habit that tends to matter most. Keeping credit-card balances from sitting near the limit, and avoiding a cluster of new applications in a short window, can also help the picture that credit reporting bodies hold about you.
What is worth checking
You can ask the credit reporting bodies for access to the information they hold. If something is wrong, you can request a correction. Sorting out an old error is often more useful than any product that claims to “boost” a score overnight.
A mixed file is not the end of the path
A past missed payment stays on a file for a period set by the rules, and then it ages off. In the meantime, a steady record of on-time payments is the slow, unglamorous way the picture improves. If you apply for a new loan, be honest on the form — a credit provider will likely see the file anyway.
This is general information, not personal advice. For official explanations of credit reporting, see the guidance published by the credit reporting bodies and the Office of the Australian Information Commissioner.