Strategy 1: Bribe the judges.
Strategies 2-infinity:
It honestly depends. Some judges look more for creativity, and others (like at some fiddlers’ conventions) won’t like it if you stray from the melody or play things that aren’t very traditional.
However, I imagine that every judge looks for a cleanly executed performance. So cleanliness, good timing, and good tone are key things to focus on, no matter your style.
Usually in a contest you play the tune through multiple times. The first time, you usually state the melody pretty clearly. The second and third times are the places for your fancier licks, and you can bring back more melody at the very end to close it out.
One of the best things you can do is listen to a bunch of contest arrangements and see how they are structured. You can watch the Winfield banjo competition, find videos from Galax and other fiddlers’ conventions, or just watch videos of @Timothy_L.
What did you play in this last contest? We’d love to hear it if you got recording as well!