It won't be purely luck based. The people who will do well are good at FFA positioning and general tactics, and will be good with items. Unfortunate things may happen, but I'm sure that the one who wins it will be one of the best in the room.
Practice item tossing, item catching, Insta-tossing, etc.
It's a tournament about finishing. Can you finish people off? Are you comfortable enough to go offstage and gimp people to steal kills? Do you know the best methods for killing with your character? If the answer to any of these is no, you have practice to do. If you can rack up damage but can't kill, you'll suck at this format. You don't have the luxury of forcing a percent lead like you do in our standard 1v1 Timed Stock Ruleset.
Edgeplay will be important. Learn how to work item properties into them. Learn throwing trajectories speeds. Learn item knockback properties.
Learn to recognize targets. Some guy just got knocked off stage? Go make sure he dies. Someone's approaching kill percents? Hound him until he's killed by your hand. Fantastically powerful item just spawned? Better go grab it.
Our normal skillset is still applicable. Move spacing, movement, staying safe, pressuring people, it's all still good. Stage positioning is made even more important in this format. You need it to grab items easily. You need it to get to your easy targets quickly.
Seriously, people, just learn to abuse the new ruleset. The game hasn't changed significantly, just your tactics. Item FFAs aren't nearly as randomly chaotic as most people think. There's a lot going on, but it's not random.