Move your user and computer objects into an OU structure, as opposed to the default Users and Computers containers.
Keep the OU structure as simple as possible.
Do not nest OUs more than 10 layers deep, and preferably keep them less than 3 layers deep, if possible.
Keep the number of OUs to a minimum, and use them only when necessary.
Apply Group Policy to members of groups through Group Policy Membership Filtering where possible.
Use domain local groups to control access to resources, and use global groups to organize similar groups of users.
Use distribution groups or mail-enabled security groups to create email distribution lists in environments with Exchange 2000/2003.
Mail-enable security groups if separation of security and email functionality is not required.
Don't simply delete and re-create groups on the fly because each group SID is unique.
Don't include users from other Mixed mode domains in a forest in universal groups.
Don't use local groups for permissions in a domain environment.
