I recently checked my credit score and, after it being bad as recent as one year ago, it is now classed as excellent. The entire reason for the transformation was that I took out a credit card. I know, I know, it can be a risky thing to do, but I limited the risk by getting a very low credit limit. Most importantly (and I can’t stress this enough) I only used it to buy things I already had the money for. I simply paid by credit card and then immediately paid off the balance – not leaving myself in debt for more than a few days at a time. If you know you have the discipline to do this (and only if you’re confident you do) this is an extremely effective way to make your credit rating healthy again.
In the UK registering to vote raises your credit score, as does being at the same address for a long period, having the same bank account for a long period and obviously paying all debt on time and in full (and that goes for mobile phone bills too). Remember, in the UK, if you live in shared accommodation your credit score is also effected by the credit rating of those you live with – so choose your housemates carefully!