make sure you have a listen to Alan Sierra's Holden. Or ford. Or whatever it is. the red thing. quite nice it is, too

also make sure you have a listen and a chat to Cory Zion, cause he's a dude and he has a crazy (as in chaotic, whacked out crazy) install in his crazy van.
Try to stay away from Spyne, as he'll probably bore you to death and make you want to give up car audio for ever.
Apart from that, just grab a copy of the
rules (especially the safety ones) and make sure you either adhere or exceed the specs.
If you havent done so already, get a copy of the judging disc. Go through each track and make sure that what the guy is talking about, your system pretty much shows off. As Spyne said, make sure the subbass
blends with the midbass and the rest of the music. If you can locate the position of the sub, its too loud. Keep turning it down just a fraction until the sound is just on the cusp of being able to hear it and feel it.
Move the driver's seat as far back and as low as it will go.
Also, dont make too many last minute changes, just to try and "get it right". At nationals last year (my first and only comp) I got someone who I thought knew what they were doing to do some last minute "tuning". He totally ruined what little staging and imaging I had, the doofus (actually I think he was jealous of my car, and wanted to see me lose

). Go with what you know. And give that stinky car a vaccum already!
Good luck
Matt