One way to improve how much revenue your store can bring in is to reach out to customers who have already bought something from you. It takes far less energy to get people who have already bought from you to buy a product than it takes to get a new person who hasn't ever heard about you to do the same. Don't forget about your older customers. You should be regularly reaching out to them and letting them know about new products and deals on existing products.
One of the best ways to maintain communication with your existing customers is to let them opt in to your newsletter. You might already have a newsletter signup somewhere on your site, but you might as well offer it to anyone who is going to checkout. Doing so during the checkout process is relatively painless since you're already collecting all of their information. You only need to add a checkbox to the checkout to let the user opt in. The programming will do the rest.
You'll need the Newsletter Subscription plugin (available on WooThemes.com) installed and activated on your site.
You'll also need to either create a Campaign Monitor or MailChimp account. MailChimp is well known and respected in the web community. They offer a free plan up to 2,000 subscribers, so I recommend setting up a MailChimp account.
In order to add a newsletter signup to the checkout page, take a look at the following steps:
You can change the default Checkbox status to Checked, but I don't recommend it. There isn't much point having a big newsletter list if people aren't interested. As your newsletter list gets bigger (2,000+), you'll have to start paying a monthly fee. It's better to let people opt in and create a highly focused and interested list.
This will save the page and will also load your newsletter lists in your account. If you don't see any lists, you either haven't created any or you have entered incorrect API information. Let's move on by finally signing up for the newsletter.
If you're using MailChimp, you'll have one extra setting, Enable Double Opt-in. This will send an e-mail to the address provided, asking them to confirm they want to join the newsletter. This prevents users from entering a dummy e-mail address and filling up your list. I highly recommend leaving this option on.
You should now see the ability to opt in to your newsletter on the checkout page.