By far the biggest value-add in terms of salary over my career has been, and this is probably very finance specific but still, having a very good relationship with a recruiter. A recruiter with a good network has massive incentives to repeatedly place you over the course of your career, and if he knows that you are a good employee then he will usually give you the context on the positions that allows you to safely negotiate raises.

You also get to learn what specific recruiter/job description lingo means, for example "position with a lot of opportunities to develop" = "the senior employee doing this job quit/convinced the management to hire a junior for this".