Stick with open source technologies that are widely used and stay on current-ish versions. Other than that, stay as close as you can to what you're doing. Like

Stick with open source technologies that are widely used and stay on current-ish versions. Other than that, stay as close as you can to what you're doing. Like if you build web apps, stay close to doing HTML, CSS, JS. If you start getting into derivative languages which compile down to or generate the base tech being used you are more likely to run into hardly used tech that becomes unmaintained or is ditched.