Look at the Melee->PM changes thread and reverse everything:
http://smashboards.com/threads/what-are-the-differences-between-melee-luigi-and-pm-luigi.365619/
As far as overall strategy goes, it's pretty much the same in both games. However, Luigi's physics are really different; you'll probably find them uncomfortable until you get used to it.
• Don't use Cyclone anywhere near as much.
• Don't ever dash attack or down tilt.
• Don't try to combo into misfire.
• Don't missile between stocks out of habit.
• You don't retain your momentum when you grab your opponent (you'll stop immediately if you were moving).
• You have 1 frame less to release the jump button to short hop, though this shouldn't be a problem with Luigi.
• You can't do the thing where you wavedash off a platform while holding shield to retain your momentum (and therefore fly really far).
• You can't RAR.
• You can't waveland fireball.
• You can't grab the ledge out of a missile.
• You can't drift after your up-B until you've fallen really far (almost as far as the distance the move sends you upwards).
• You can't rise from a grounded Cyclone.
• You can't get very much off a Cyclone, except maybe a tech chase sometimes. Even though it still clanks like it does in PM it's way less safe in general. Against fastfallers with bad DI at specific percentages, you can sometimes get a combo from it (second hit into up tilt/nair/down smash).
• Aerial up-B sweetspot is far more situational because of its lowered knockback. It kills roughly 10-20% earlier than a strong nair, depending on the situation.
• Your recovery options are a lot more limited.
• You can jump cancel your dash to up smash from it (in the same way you do to up smash out of shield).
• You can lightshield, which is something you should go out of your way to incorporate if you're going to be playing Melee at least semi-seriously. It's the kind of thing that can get overlooked easily.
• The invisible ceiling glitch exists.
• Habitually use a grounded Cyclone after taking a stock to charge it. Read this thread for details on how charging works:
http://smashboards.com/threads/rising-cyclone-ptp-frame-data-guide.384946/