Luck certainly plays a part, but just knowing what you're doing and drafting well is the biggest thing. I haven't missed the playoffs in a league with money on the line since 2016.
I credit that mostly to starting dynasty that season. As such, I became a lot more familiar with the entire skill position groups of most teams in the league, and that knowledge carried over into redraft, as it's easy to hit on some sleepers every year when you know every situation in the league and who has the chance to break out or who is one injury away from smashing.