How to make sure the site is as secure as possible?

What would you recommend to make sure the site is as secure as possible.

To protect a website you need to:

1) Fix all vulnerabilities in website engine scripts. Minimum: upgrade all third-party scripts to latest versions. Maximum: make a source code security analysis.
2) Use latest stable versions of server's software (web server, ftp server, mail and etc).
3) Use of Dedicated or Virtual server is more safe also. If neighbour websites (on the save server) are vulnerable then your website may be compromised also.

Alex.
Website Pentester.