Your best bet will be to give away something that’s valuable to your target market; for instance, a high-value digital asset on a niche topic. You can give away products (we’ve all seen contests where the prize is a free iPad or gift certificates), however this strategy often leads to entrants who are more interested in the money than in what you have to offer.
Unfortunately, there’s a bit too much depth to the topic for me to cram everything in to a single blog post. Therefore, I’m going to begin creating a multi-part blog series on list building. Over the next couple days, I’m going to purely focus on teaching some tricks of the trade to build a list quickly (these have now all been merged into this single post).
It’s a best practice to ask the referrer not only for a friend’s email address, but also for a full name so that the message is personalized. Most important, remember to add the referee’s full name to the email as well. By referencing whom the email content was recommended by, you gain instant credibility and will attain much higher conversion rates.
For effective and actionable results, you should do A/B tests, which test two (or more) different approaches. For example, you could send half of your list one subject line, and an alternate subject line to the other half. You could also A/B test the two approaches with a small subset of your list, then send the winning headline to the rest of the list.