Know-How Exchange : Copywriting

Relevance of message and offer to the recipient.
Salience of subject over other in-box content.
A commanding headline that demands attention.
Short line lengths.
(Like this).
Compelling copy that speaks to the user's problem or need.
Subheads that tell your story in short soundbites.
A powerful offer that's too good to pass on.
A solid call to action.
Benefits.
More benefits.
Even more benefits.
Value.
More value.
Scarcity.
A deadline.
Reasons why the recipient ought to respond right now.
A working link (that you've tested and retested).
A recap of the issues and your offer.
A sign off.
A solid, hard-as-nails guarantee.
A postscript in which you repeat the offer and the link.
An unsubscribe link.

Fin!

Hire a professional, experienced copywriter and discuss your issues in-depth with him or her.

Write your copy from the perspective of your reader. How do you help solve their problems or achieve their goals? Why should they trust you? And cotinually measure your efforts to learn what people respond to (A/B split test, for example).

I'm with Mike Steffes: Hire an experienced professional copywriter.

Copywriting is an art, and it takes time/experimentation to develop the skills to write compelling copy. If the task is important, hire a pro. If it isn't important, then just do what you think is best, with or without tips and lessons from a course. It probably won't matter.

If you don't really have an option, then the advice offered by Gary and Jay is correct.

if you can't afford a writer, at least have your e-mails reviewed by a competent editor. For example, your post said “companies” where you should have written “company's”. You cannot build credibility among American buyers while making basic grammatical mistakes.