Originally Posted by Bud Helms
Don't use them if there is ambiguity in their use.
Try not to use them at all. Then there is no problem with the reader understanding what they mean.
What good advice...
But when you come across a potentially ambiguous acronym, context can also be your guide: If someone puts "FTF" in a thread title in the "For sale..." forums, it's a pretty safe bet that they don't want to ship whatever they're selling. If someone in the semi-auto handgun forum starts a thread titled "FTF with Glock 19," it's a pretty safe bet that they're not talking about getting up close and personal with it.