My buddy and I entered our first competition a few months back. We just entered beers we happened to have in unlabeled bottles, none brewed with a comp in mind. He finished 3rd in the other category with a wheat based stout. Mine was rated good, a 26 I think, with some flaws, which I knew going in. It was an ESB that I just kinda whipped out without a fine attention to detail. It's great getting feedback from non-partisan reviews. It reinforced what I already knew (mash temps, oxidation etc.) I now put greater focus in controlling temps and making sure I introduce as little oxygen as possible when transferring from the carboy to bottling bucket.
Good luck!