Don t waste your subject line. Don t ever leave the subject line of your email blank, but don t waste it by just inserting the job number. Instead, use the subject line to entice the reader into your cover letter. Your opening paragraph is critical. Keep your cover letter short.
Brevity is critical with an email cover letter.
Focus on your key selling points. Most experts say that at most, your cover letter should be two to three paragraphs - and under 150 words. The idea is that your cover letter should not be any longer than one screen in length. Take advantage of keywords. Use keywords pertinent to the job you are seeking, and focus on key industry buzzwords and critical skills sets.