If you want people to use (or share) your service then learn what makes people tick by reading good books on psychology.
A great primer (also for advanced marketers) is Robert Cialdini's "Influence". Buy it here and never look back.
People don't have much time to read emails. Keep it to 3-4 sentences at maximum, in separate paragraphs for easier reading.
For your emails to have a chance of getting read, they need to...
For both points, putting the recipient's first name in the subject line (and the body) helps: Filters see that you're addressing a specific person, thereby classify it less likely as spam, and secondly your recipient feels much more compelled to open the email, without which even the best email content is worthless.
If you don’t receive the email in the next 2 minutes please check your junk folder, and add [email protected] to your safe sender list.