This is exactly the kind of process that, because there's so much room to play around, results in multiple solutions that could all be considered reasonable. You might not find a "standard design". You should just use the simplest version that you will work for you.
Take a look at RBAC (Role-Based Access Control) products. RBAC systems, for managing users by assigning them roles and access levels, will have a lot of the UI constructs you are looking for. i.e. create a group (role) and assign items (users) to that role.
I've worked on a basic RBAC we built for internal use. I've provided an overview in the wireframes below.
There's not a lot to it. The key design decision we made was to go with the "layered page" approach to interacting with existing groups. i.e. in the last wireframe below, the user has clicked to edit a group. In this case, the group appears as a "page" layered on top of the main list UI. This is a pattern we borrowed from the Basecamp project management app. The user can interact with the group and get back to the page beneath by either clicking the 'X' or the title of the deeper page (i.e. 'Groups') which has become a link.
You can achieve quite a lot with a carefully applied mix of page layers and modal dialogs.
download bmml source – Wireframes created with Balsamiq Mockups