So another year down and it seems the judging is still controversial as ever. Anyways, I've judged at Expo since I was 14, so here are a few tips on what I look for in judging your models.
1 - Reference..ah yes lets get this one out of the way first. If you supply nothing, you will get 0 in the pre judging form, that means you miss out on 25% of points possible and your chance of progressing to the technical stage is almost non existent. To give you some idea of how cut throat this stage can be; I judged a category with 38 models in it, only 1 model that did not score 100% (that is 12 out of 12 points) progressed to the technical judging. Out of 6 kits that scored 11/12, only 1 progressed. This is only a quick overview of the models to spot obvious errors, so if you have a very prominent panel line showing, this might just be enough to cut you. Keep this in mind.
2 - Leading and trailing edges of wings. I can't count how many models lose points for this. I've even knocked out models in the pre judge for this reason. Make sure you fill and sand those edges.
3 - Tank wheels, make sure they all touch the ground or are in contact with the track at the appropriate point. Having two or three wheels that randomly sit off the track when your tank is meant to be sitting on a flat surface will almost certainly knock you out in the first stage of judging.
4 - Finish and paint the bottom of your tank/ship/aircraft. I picked up one very nice model on Saturday night, only to find the modeller had not bothered to fill, sand and paint the bottom of his kit. Yes I will pick up your model. If you don't want to paint the bottom of it, then glue it to a base, but be warned, some judges carry little detail mirrors and lights. You might not always get away with it.
I hope this helps you build a better model if you are actively going after a trophy next year.