Don't pay too much attention to that actual score out of 100 that experian do. You have to remember that people at the top are company directors borrowing big sums of money and repaying over short timeframes.
As long as your not getting turned down for applications, what's the problem? You're going to hit a glass ceiling with the score because you are only 18 anyway. As you get old, get a mortgage and keep paying off existing credit that score will increase, but there isn't really a magic way, and taking out other forms of credit when you don't really need them increase a number is daft.