This comes from a newsletter for writers:
New Yorker magazine editor, Alice Quinn, reads from the new Elizabeth Bishop book, April 27
Those commas around Alice Quinn are as unnecessary as feathers on frogs.
Here's our trick for remembering when to use them:
If the meaning of the sentence depends on the information you're considering wrapping in commas, then don't use the commas.
In this case, the particular editor in question is essential to the meaning of the sentence. Without "Alice Quinn," it's not a complete sentence. It would be if it were changed to "A New Yorker magazine editor reads from the new Elizabeth Bishop book," but it wouldn't tell you which editor. We need Ms. Quinn in there to know what we're getting at the reading.
If the sentence retains its essential meaning without those words, then do use the commas.
Commas, like feathers on frogs, are only used to set off non-essential clauses. (Grammarians call those "non-restrictive," which we find hard to remember.)