1) Focus on plot. This was the biggest mistake I made the first year I entered. I didn't realize how important it was to make those 15 pages really count. It's not enough to have dialogue--even interesting dialogue--that builds character, the kind of thing you would have halfway through your novel. You need to hook the reader now more than ever, and you do that through showing the stakes of what the character has to lose.
2) Focus on voice. Though plot is important, it's not going to sparkle without your voice. Go through your entry to find sentences where your voice really pops. Then figure out a way to highlight those sections. Either do some rewrites to highlight your voice, or emphasize those sentences by putting them in high-impact places, like at the end of section breaks. Be intentional about your wording, descriptions, and pacing.
3) Focus on detail. Details matter. Pay attention to the rules and regulations of the contest--where your header should go, what should be included, how you should format your synopsis, etc. These little things are--let's face it--boring, but they tell your judges you care enough about your entry to take time to make every little thing right, and they'll keep you from getting unnecessary point deductions.
What other things have you been focusing on as you've been preparing your Genesis entries? What are you nervous or excited about as you enter these kinds of contests?