Before the interview:                                

Research the organisation, check the company website and search them on the internet
If changing career/industry, research the industry
Prepare answers to standard interview questions
Make sure you know the name of the person or people interviewing you
Check the format of the interview
Check the formality of the interview and prepare an interview outfit
Print out spare copies of your CV to take with you
Re-read CV
Plan the journey to the interview
Check the news/traffic reports to make sure there are no problems
Take a contact number for the company with you in case there are any problems
At the interview:

Switch off mobile phone
Ask when you can expect to hear back
After the interview:

If appropriate, email to thank the interviewer for the opportunity
If unsuccessful, contact the interviewer and ask for constructive criticism/feedback