Do certain pages seem to lead to more sign-ups than others?
If so, you can examine those pages and try to figure out what is making them work better than other pages. Perhaps you have a better call-to-action on that page. Or the subject of that page is more conducive to encouraging visitors to sign-up. You can take what you learn there and apply it in other areas of your site to increase your overall conversion rates.
Do certain sources (channels) such as organic search, paid search, or social media have better conversion rates than others?
If so, then you should consider shifting more of your resources to that channel to get more conversions. You can also look at the channels that are not performing well and see if you can improve the messaging there, or check to see if that channel is an appropriate channel for your offer.