When you make an application for a loan, credit card, mortgage or other type of credit (such as a new utility contract or mobile-phone account), lenders look at your credit report to decide if you'll be able to make new repayments on time, to calculate your credit score, and to assess any potential risk of lending to you. They may not expect you to have a perfect credit report, but they do want to know that you will make repayments on time and that you aren't already over-stretched.
Your credit report is essentially an overview of your borrowing behaviour. There's information that confirms your identity - such as electoral roll details - information about previous credit applications you've made, and there's financial information, such as a list of your credit accounts and repayments. So it pays to make sure it's up to date and accurately reflects your circumstances, and query anything that isn't - as mistakes can hurt your credit rating.
Pay particular attention to personal details, such as your name, address and date of birth - even minor mistakes could lower your rating. If you find an error, contact the relevant lender and ask for an amendment. Watch out for unfamiliar or suspicious entries in your credit report as that could indicate identity fraud.