Watch Blea Gelo, Abate, Eddy Mexico, Vist, and Vudujin. That's basically it.
And my favorite old school player of all time made this... pretty cool
https://www.youtube.com/watch?v=bn7ZdA-dTx4
Learn your tech skill, l-canceling and fast falling (when necessary) every time, fast falling into perfect wavelands, ledgedash (ledgehop to waveland on stage) into various moves like utilt, ftilt, usmash, dsmash, etc... learn luigi's hitboxes.... look at the frame data, and more importantly, play multiple games to learn them inside and out... then figure out your general best approaches, and apply them as effectively as you can. Learn luigi's recovery... and pay attention to how the best luigi's edgeguard different characters!! matchup knowledge means a lot.
Pacman and Smash G0D also wrote a lot of great stuff on the luigi boards years ago, I'm sure you could find it... and if you want even more videos, lol... there's KA-master, ultra luigi, ROFL, and a few others but those are really old school. I think ROFL might still play.
