Do not merely read through your CV. An interview is an opportunity to deliver all of the skills you have that your CV can not express.
Put on a nice suit. Be smart and neat.
Say thank you to your interviewer at the end and after by email or send a 'thank you' letter by post.
Try not to oversell who you are.
Interact, perhaps, with the firm's twitter profile.
Create a Google Alert on the employer to know latest developments.
Advice for Job-hunters:
"Subscribe to a trade publication or some type of magazine that specialises in the sector you are seeking employment for. This will ensure that that you are abreast of any changes in the sector. This will be helpful in the interview to show the potential employer that you are attentive."
It may be helpful to have:
Flexibility
Being eligible to work in the United Kingdom is mandatory