Wood pretty much nailed it on the head (no pun intended) but here's a couple other things to keep in mind.
Platforms are extremely useful for warp canceling, but keep in mind your offensive pressure options too. With the new shield stun changes, I've found that nair and short hop uair is now surprisingly safe on someone sitting in shield on a platform. If all they do is just sit in shield once they reach one of those platforms within your short hop or even full hop range, don't be afraid to put on the pressure. All the hits of nair connecting does put a bit of pressure on their shield and I managed to break shield with uair in a match before (granted this was when my opponent's shield was already super gone but you get the idea). With platforms, try your pokes. Throw out an up smash to get them off the platform, nair/uair their shield, general platform pressure will make them think about trying to approach above you. Also practice your shield drops for the best results; you wouldn't believe the amount of times shield drop uair has saved my skin against rougher match ups.
Another thing to consider is the cost of going to low ceiling maps, mainly T&C and Halberd. Both are absolutely killer maps for Palutena, in fact I contend that Dreamland and T&C are tied for her best map. However the low ceiling on both the maps I mention come at a bit of a price. Uair gets a ton of mileage on these maps, but keep in mind that Palutena is still pretty light. Sure she can kill off the top on Halberd as early as 75%, but she can also die even earlier to someone with an even greater aerial game *cough cough rosalina cough cough*. These maps are awesome, but to make them awesome you have to be on point with your play and you have to always keep a mental note of that ceiling. If you face someone like ROB or Rosalina, someone with a killer aerial that can get you up there quick, be on the defensive and respect those aerials. So to get the most out of low ceilings is simple; outspace your opponent and don't let them get close even once. Do that, combine it with a good punish game, and respect the ceilings.
As for some of the other maps, mainly FD and Duck Hunt, I would try to avoid those maps. Duck Hunt would actually be the preferred choice in this case because the layout allows for her autoreticle to get some good use and the trees make for good spots to bait a chase up top where you can catch people with some tricky stuff that could lead to a kill.
So for applying this in a tournament setting, I'd say try to go T&C or Dreamland for the first match as much as you can. If you win, try to influence Delfino or Lylat for the counterpick. If you lose first game, go for Halberd or Lylat. Throughout the set, general rule IMO is to try to avoid going to FD, Duck Hunt, and Smashville. And for the love of all that is holy, never agree to gentlemaning Smashville.
