1) Make sure you are on the electoral register. If you arent, you'll find it difficult.
2)Make sure you have your name and current address correct on anything you have. Drivers license, Bank account, Utility bills
3)Not having credit, makes it difficult to get credit. Crazy i know!
If you dont have one, get a mobile phone on a contract (pay monthly) and make sure you pay it in full,and on time. Thats the easiest credit to get. It doesnt have to be an expensive contract, �10 will do.
Also try a store card, they tend to be easier to get than a credit card. Buy something on it, doesnt need to be much, then pay it off immediately so you dont get charged interest. Keep doing this for 6 month- 1 year to prove you pay back what you borrow.
Thats the best way to build yourself a credit record.