Adding an opt-in box to your blog offers another opportunity to provide value for your visitors.
In exchange for your free gift, newsletter or other product offers, you can ask potential clients to sign up by providing their name and email address.
By adding an opt-in box to your blog, you are providing visitors to your blog (and therefore potential clients) a further opportunity to sign up for your free gift.
You can find further information on inserting an opt-in box to your blog here:
Blogger > "14. Creating An Opt-in Box" and "15. Adding An Opt-in Box To Your Blog"
Adding a pop-up box to your blog page will prompt any visitor to your blog page to sign up for your free gift. Paul provides full information on how to add this pop-up box here:
Blogger > "15. Adding An Opt-in Box To Your Blog" > From 5'30".