The first step is building genuine relationships, because that amplifies the second step, which is information gathering. The strategy for an employee should be ask for promotions as fast and often as humanly possible without pissing off your boss and management. It can be an awkward question just asking other people how much they make but if you're friends with them it makes the conversation a whole lot easier. Knowing what the market rate is for the roll above you is probably the hardest piece of information to ask for.