I would download some of the trials or the RTPs and familiarize yourself with the sort of graphics that the program needs so you know what sort of things people are going to be requesting and how to format the files and such. I mean, a lot of people on this website aren't artists and they aren't going to have art programs or specific knowledge in art programs. So if you understand the basics, you'll be better off at giving what they actually NEED in a file, rather than just an artwork that they need to figure out how to usually shrink and format into a file.
Knowing the basic, default dimensions and formats is just really helpful. Even just a small bit.
Though, I guess if it's strictly concept art and not the actual resources that are going to go into the games (face sets, busts, battlers, battlebacks, etc) then that matters less. Though, we're talking in a community where people do not tend to have the $$s to toss on concept art first AND their final product that's going into their game - so that's a heads up I suppose.
A lot of the hit and run classified threads that did pop up before the rule went into place were just showing big shiny artworks and not showing how that artwork is going to integrate into an RPGmaker game. It wasn't showing things that people were going to actually going to be able to USE in a game. Very few people on here have the money to function like a AAA game company or even like the bigger indie devs; concept art on a whole is a largely foreign thought.
Also! like mlogan said, having a presence, face, and personality on the forums is going to help drive business. So, in the long run, interacting with the people here is good for that. It doesn't need to be making games - commenting on other's art, taking on requests in the request threads, watching the classified requests for things you could do, showing active reception in the game thread of a game that you DO get hired to help with, etc, etc The more people know your name - the higher chance they'll think "Maybe I want MezioPleo to do the art for this game!" when they're thinking up a new project.