Know the service account characteristics. Ensure that you know what types of service accounts are available and which are appropriate for each SQL Server service.
Know about service packs and security updates. Know where to find out about current patches and updates and have a strategy to apply them to your systems.
Understand the SQL Server 2005 encryption hierarchy. Be sure that you understand the encryption hierarchy in SQL Server 2005 and how the service master key and database master keys are used.
Know symmetric versus asymmetric keys. You should understand the difference between symmetric and asymmetric keys and where each is best used.
Be comfortable with server and database roles. Be sure that you understand the different roles, both fixed and user-defined, at the server and database levels.
Understand the principle of least privilege. Know what the principle of least privilege is and how to apply it to your security model.