Your credit report is what lenders look at to decide if you are creditworthy to lend to, so it is imperative that your credit report is accurate and improving your score is essential to obtaining the best deals.
Make sure you check your ratings on a regular basis, most lenders go to two main credit reference agencies, Equifax and Experian. These agencies keep your credit history including current liabilities you have, previous debts, County Court Judgements, electoral roll amongst other data.
Every time you take out a form of credit it will be registered with the agencies and they monitor how you conduct your finances.
The agencies and the lenders, using many different factors, will give you a credit score. It is not the credit reference agencies who decide if you are accepted or not, the lenders will carry out a credit search and will using their own criteria to give you a score. The higher your score the better your chance of being accepted.
There are ways to check your credit report for free, Experian and Equifax offer 30-day free trials of their service online but you will need to remember to cancel before the end of the promotion to avoid subscription fees.