There's an old joke (popular at least in New York, back in the day). Newly arrived tourist to local: "How do I get to Carnegie Hall?" Local to tourist: "Practice, practice, practice."
I can't say how to reach guru status, not having gotten there myself. I suspect it involves working for the tech team that produces one of the solvers. To get to what I might call "power user" status, you need to use the solver repeatedly, starting with easy to formulate models and progressing to models that involve advanced techniques (decomposition, column generation, mysterious oracles, ...).
Things that have helped me get where I am today vis-a-vis CPLEX, in no particular order, are:
- Using it ... a lot.
- Using it with a programming API. APIs require you to attend to details from which modeling languages (such as OPL, MPL, AMPL, GAMS etc.) might shield you. I personally don't think you need experience with more than one API, although it certainly does not hurt. When programming, if something in the API documentation seems unclear or unexpected, take some time to chase it down and see if there is a (possibly hidden) reason why it is the way it is.
- Monitoring the relevant help forums. (I subscribe to the CPLEX forums via RSS feed.) Not only can you get your own questions answered, but you can learn tidbits about the internals from seeing the answers to other peoples' questions ... plus you can find out where people get confused by the solver.
- Watching for solver-related questions and answers on forums such as this one.
- Experimenting, as time permits, to see if you can figure out the answer to a question (or the source of an error message) when someone asks something not particularly mundane on one of those forums.
- Attending conference workshops (and occasionally presentations in technical sessions) by the vendor. IBM, Gurobi and (I think) FICO put on workshops at some conferences, including the INFORMS annual meetings.
- Stopping by the vendor booths at those conferences and chatting up the technical folks.
- Attending (or watching after the fact) vendor webinars. I know that IBM and Gurobi both have periodic free webinars on topics related to their solvers, and I'm pretty sure I've seen FICO webinars listed.
I'm not sure that list is exhaustive, but it's all I can think of at the moment.