As an almost complete beginner how would I get to the point of being able to consistently find security issues where they exist? I've got enough experience as a

As an almost complete beginner how would I get to the point of being able to consistently find security issues where they exist? I've got enough experience as a developer to avoid the most common vulnerabilities, but I don't really know how I'd go about approaching things from the other direction to surface potentially undiscovered issues.