It's important to understand the intended role of each group type. These users and groups must belong to the same domain as the global group. In mixed mode, global groups can contain users from within the domain. They can also contain other domain local groups from the same domain the group resides in. In mixed mode, domain local groups can contain user accounts and global groups from any domain in the organization.
Universal groups exist only in native mode.
Let's look at some techniques for implementing global groups and domain local groups. I recommend assigning users with similar jobs to global groups. For example, within the IT department, you might have a Programmers group and a Network Support group. The next step is to create a domain local group for each shared resource or group of shared resources. Likewise, if you have a shared printer, you might create a domain local group called Laser Printer.