Darren,
My first advice would be, go to the contest not expecting to win, but to have a good time. Meet other modelers, admire other builds, and look for deals in the vendor area. However, completely forget about the model(s) you've entered. You'll have a much better time.
I realize that most people really can't do what I've suggested and will wonder about their models and worry about what they can do better to earn an award. Notice that I don't say win, but earn. While many modelers see contests as events where someone "runs to the front", in reality, just the opposite is true. Modelers fall to the rear.
As a Contest Director and Head Judge, I've had ample opporunity to evaluate what it takes to get noticed. The first thing to remember is that for the most part, you DON'T want your model noticed right off the bat. Usually, a model gets noticed by judges because of something glaringly wrong...not because it is unusually great. There are exceptions, but this is often the case.
The bottom line is that judges are looking for errors and not for things done right. Cuts are made in each category based on problems the judges find...silvering decals, seams showing, alignment issues, poor finishes, glue marks...the list is endless. For your model to make it past the "first cut" you need to ensure that all these obvious problems are eliminated.
Once judges have eliminated all the models with problems, they will start looking at models side-by-side (in a 1-2-3 contest). Now is the time you WANT your model noticed. Judges will look at things like relative difficulty, exceptional use of aftermarket parts (PE, etc), unusual or exceptionally well done finishes, flawless scratch-built parts, attention to detail...again the list is quite long. However, these are the types of things that will earn your model the respect of the judges.
I'll repeat at this point that the bottom line for every modeler should be to enter a contest to have fun and not ask themselves "what if" questions for the next month.
Enter a contest and if possible, volunteer to be a judge. IMHO judging models impartially is one of the best things a modeler can do to improve their own ability to build for contests. And of course - have FUN!