On first use in a document:
For well-known acronyms, use the acronym first. Favor putting the full word or phrase in parentheses after.
For acronyms that are not well-known, put the full word or phrase first and the acronym in parentheses after.
On subsequent uses in a document, favor the most commonly-used form and use discretion to favor readability. For example, “HTTP” is much more common than “Hypertext Transfer Protocol” (18 billion Google search results vs. 7 million, respectively).