This is also know as permission marketing. (When your visitors are actually giving you permission to send them emails to them tell them more about what you have to offer.)

Here are some ways you can increase your numbers and build up your list.

Put in more opt-ins boxes in your salesletter. Making sure that you have one near the top and the bottom.

Bribe them with free stuff of value. It’s a value exchange society. Deal with it.

Use a resource box in your ezine or newsletter so that you can allow them to rip off your content and still get credit for it. Remember to include your website url so that you will at least get a backlink.

Set up joint ventures with other publishers. Give them a good reason to distribute your content. Give them a report for free that they can use to send to their subscribers and/or make money from it. Think win-win. You get to build your list with it if you include some of your links in the report back to your website.

Get yourself listed in ezine directories. Google for them.

Co-registration. Buy the traffic you need to kick start your list engine if you have the means to do so.

Article marketing. Write up some good quality articles and send them to article directories. You get to establish yourself as an expert in that niche and build trust before others even come to your website.

DHTML popups. Use pop ups that can’t be blocked by browsers. Sparingly. Do not irritate your prospects.

Set up an attractive affiliate program to entice people to promote your products. Use Clickbank.

Use viral devices such as tell-a-friend scripts and viral ebooks to spread your content like wildfire.

Use Google Adwords to instantly get targeted traffic to your website.

Last but not least, you can use a combination of all the above techniques to dramatically increase your opt in rate.