Keep the subject line and pre-header short: The subject line is crucial. Keep it short so the reader knows exactly what the email topic is about. And the pre-header text (also known as snippet text), don’t let it go to waste by using “To view this email in your browser…”. Instead, summarize the email or include a call to action (i.e., Use “FREESHIP” to get free shipping).
I've been using Solo Ad Advertising for about half a year now... It was the most responsive advertising I EVER used in terms of RESULTS and, by this, I mean signups and SALES not just clicks on my solos... I used Solo Ad Advertising to promote other ad exchanges and, once, for example, I had a referral upgrade ratio of more than 12%, much better than the general upgrade ratio of that ad exchange... Using Solo Ad Advertising to promote other Ad Exchanges helped me A LOT to earn hundreds of dollars from my referral upgrades and purchases and also from scoring on the top 3 of some referral contests.
When it comes to deciding how to craft that perfect subject line, there appears to be really only one area to avoid: the subject line of 60 to 70 characters. Marketers refer to this as the “dead zone” of subject length. According to research by Adestra, which tracked over 900 million emails for its report, there is no increase in either open rate or clickthroughs at this 60-to-70 character length of subject line.