An unfamiliar acronym or abbreviation that will appear numerous times in a document should be clarified by enclosing its unabbreviated form within parentheses after its first use:
The aims of the WRC (Women's Relief Corps) were to aid and memorialize the GAR (Grand Army of the Republic).One liter contains one dm3 (cubic decimeter) of water and weighs one kg (kilogram).
Placing the unabbreviated form first (and the acronym in parentheses) is not incorrect, but it may inhibit reader comprehension since the acronym will not be enclosed in parentheses in the remainder of the document.
Obviously, it is useless to introduce an acronym with its unabbreviated form if it will only be used once in the same document.