One line catches their attention: Advice For subject lines and Titles

From Constant Contact:

If your customers were fish, subject lines would be the lure:
One line catches their attention.

Did You Know? A great subject line is irresistible to your contacts — it helps
get your communications opened and read.

• Short and sweet — Use five to eight words, and no more than 40 characters.
• Do it last — Write your subject line after you put your message together.
• !@&!? — Avoid exclamation points and symbols — these are typical of spam.

Constant Contact has quite a few services including free webinars