Local HTTPS
I’m not going to extol the virtues of encrypting your site and enabling HTTP/2. The advantages should be pretty obvious by now. The real issue is that when you’ve got your site(s) and your clients’ site(s) encrypted, you’re left with local development versions of the sites which are now at odds with the live version. And it’s always best to mirror your dev and live environments as much as possible to avoid those last-minute deployment panics. Like when I deployed the all-new Clearleft site only to find I hadn’t updated the image links to HTTPS so none of them loaded. Queue a frantic 10 minutes of find and replace throughout the site templates while people were telling me the site was b0rked. Fun times.