Abbreviations and acronyms must be marked with their corresponding label, at least the first time they are used in the text and, this first time they are used, their meaning must be expanded in the text itself. For example, "The UN (United Nations Organization) has decided...". Also, abbreviations in table headers should always be marked. Another good practice, which we can import from the traditional paper edition, is to collect in a list, on a separate page or on the same page, all the abbreviations and acronyms so that the reader can refer to it in case of doubt.
I think that all of the above is quite clear and easy to do, but what causes a little more difficulty, for some authors, is knowing how to clearly differentiate when an abbreviated form should be labeled as an abbreviation and when as an acronym.
Many people fall into the error, reflected in some dictionaries, of believing that the difference between an abbreviation and an acronym is that the word it forms is or is not pronounceable in itself. But as we have seen, this is not so.
The trick or the clue to know if an abbreviated form that we are going to use is an abbreviation or an acronym is to see if we translate it or if we pronounce it directly or its acronym. Namely:
Abbreviation: The word that is created with the abbreviated form is not read, its meaning is translated, for example, when we find "etc." we don't read "e - te - ce", we read "etcetera". Also, the abbreviation "Austral." which can be used by an author to refer to something "Australian" or something related to "Australopithecines", although it is pronounceable in itself, it must be translated as indicated by the author in order to understand the text that is being read, that is, we will pronounce when finding it "Australian" or "australopithecus" as indicated by the author.
Acronym: We read the word that is created with the abbreviated form or the acronyms that make it up, as it is written, for example, "FBI" is not pronounceable, we read each of the acronyms that make up the abbreviated form, we read it as "Efe - be - i" and, "ONU", if it is pronounceable, we read it as "onu".