If I have an article or blog post and I have an abbreviation or acronym such as SAD (Seasonal Affective Disorder) should I do this everytime the acronym SAD appears in a document?
<abbr title="Seasonal Affective Disorder">SAD</abbr>
If you do only define it once, does it have to be the very first time the abbreviation appears or could it be the 3rd or 4th time?
As per Wikipedias Manual of Style you should only explain an abbreviation once. I would extend this to your case as well and only use the abbreviation on first occurence.