Do ur homework, research the company, know what their vision, goals and objectives are...

Match their corporate image (ie if its a suit environment, wear one)...

Have good evidence to answer their questions...

Be 100% on how you match the Person Specification...

Make sure you have questions to ask them at the end of the interview...

Make sure ur Facebook account, Twitter account and/or Linked In accounts don't have inappropriate info on it because that's the first place companies will look if they want info on you

Don't ask about salary and/or holiday in an interview, it's not appropriate at this stage

Be confident, smile and good luck