Make sure that your main CTA button is constantly available along your site, have one at the top, another in the middle and in the bottom of your landing page. This way you are incentivizing visitors to click on it after they have interacted for a while with your site. Repeating these buttons give your visitors extra options, especially when you have a long landing page, making it easier for visitors to find and use signup forms. Take a look at this guide to perform this hack.