Check your recent twitter messages are professional.
Don't be late. Plan for delays.
Make a Google Alert on the firm to know latest developments.
Read up on the company, hiring manager, and their history.
Suggestions for those looking for employment:
"Your CV will not earn the gig on its own. Its 'job' is to earn an interview. Make sure your CV will arouse the employers’ attention so that you can get the first interview - and then that is where you can earn the job."