Database Mirroring Setup Steps

You need to perform the following prior to start database mirroing:
1. Take a full backup in principal database and copy it to mirror server
2. Restore the principal database using With NORECOVERY option
3. Take a single transaction log backup in principal servers database and copy it to mirror server
4. Restore that single t-log backup using With NORECOVERY option and start mirroring,
it should work..

SQL Server Agent jobs setup minimum permissions

SQL Server 2005 introduced the following msdb database fixed database roles, which give administrators finer control over access to SQL Server Agent. The roles listed from least to most privileged access are:
SQLAgentUserRole
SQLAgentReaderRole
SQLAgentOperatorRole


http://msdn.microsoft.com/en-us/library/ms188283.aspx

To find out users and roles on SQL Server Instance

--users and roles on SQL Server Instance
sp_helplogins