Please don't assume that readers will understand your acronyms and don't make them break from your story to look them up. If they bother to look them up, once they leave your page, they may not come back. Or they could just click out of your story because they can't be bothered to look up the acronym. Acronyms should be spelled out at first mention in the story, followed by the acronym in parentheses. After that, the acronym alone can be used. If the acronym is not repeated, just spell it out when you would use the acronym. Does that make sense?