I haven't had the opportunity to try it, but a suggestion I liked when I heard it was to go to the person in a position to give you a raise and tell them "in six months time, I would like to be making X$. What would I need to do or show I am capable of doing (actionable, measurable, objective is important here) for you to give me that?"

Then do those things. In six months, remind them about the conversation (I'm sure it'd go better if you had a reliable way to jog their memory, eg email). If you're worried about them backing out, maybe follow up halfway through to see if they agree that you're on course and that they understand you meant it.