I was taught to use the full name of an organization the first time it's mentioned, then if you wish to use the acronym later, put it in parenthesis after the first use of the fullname.

Such as "Margaret Taylor-Greene (MTG) addressed the Valdosta White Citizens League (VWCL)." Then later "VWCL endorsed MTG after her speech."

Now too often reporters only include the acronyms with no in-article definition. That's OK for something like the UN or USA, but not for the myriad of other obscure acronyms floating around.