Before deciding to buy you will need to know that your credit score will allow you to access a mortgage product that will allow you to buy.
You can check your credit score for free at Noddle.co.uk
This will give you an indication of what information is held by credit rating agencies who mortgage lenders will use to give them an understanding of the level of risk that they are taking on by lending you a large sum of money you will need to buy your first home.
Developing an 'excellent' credit rating will allow access to better value mortgage products as you are seen as being less risky and more likely to not default on the loan.
That old phone contract that you forgot to pay, maxed out credit cards and short-term loans are all things that might be detrimental to your score so understanding what the credit agency has on you in advance will allow you time to make sure all your details are accurate.
If you have ever been declared bankrupt, been subject to Individual Voluntary Arrangement (IVA's) these can be seriously detrimental to your chances of getting a mortgage, however, there may be lenders willing to offer you a mortgage product. However, due to the higher risk, this presents you may find yourself paying a higher interest rate.