Always on SSL
In order to get the most out of your SSL and increase your rankings potential it's important that you enable SSL encryption across every page of your website. A lot of times sites only put HTTPS on the pages that need it—don't do that. Google serves results on a page-by-page basis—not by your site as a whole. It displays the most relevant page. So to get the added benefit of having SSL as a ranking signal, it needs to be on every page. You may have a really great blog post about a specific topic that does very well on its own, but it won't get a boost from SSL if that page isn't served over HTTPS.
And keep in mind, it's not like you need an individual SSL/TLS certificate for every single page, either. One certificate can secure your whole site–every page. It all comes down to how you configure your server and whether you have the right security solution. If you have multiple sites you need to make sure you have a Multi-Domain Certificate. If you have Sub-Domains like mail.website.com or login.website.com, you need a Wildcard certificate. But, as long as you have the correct SSL solution your whole site (or sites) can be secured with a single certificate.