I don't want to dismiss what PORTERHAUS has said as I don't really disagree. However, you'll find the judging will vary significantly so at some point it's not worth worrying about. Give your beer the best shot you can, and then understand there's nothing else you can do. I just got a gold medal for a beer that was destroyed in the NHC First Round. In another comp the same weekend, it scored a 22. Such is life.
I am coming to believe that at a certain point in an advanced homebrewer's career, entering competitions becomes a very low value, diminishing returns kind of thing. I might not enter any competitions anymore, I'm not sure. When you can criticize your own beer 10 times better than anyone else can, it might be time to save the money. Now...... if competitions were free to enter, then maybe that would be something.