It's somewhat tricky but you basically just have to fastfall (aka press down on the movement stick) right after you throw out the attack. You want to do the attack just at the height of your jump so you can fastfall afterwards (especially as you can't fastfall on the way up for whatever reason).
It's kinda confusing because you'll see the glint that shows you fastfalled before you see the animation for the attack come out XD
If you do it right though then you'll actually kind of 'strafe' the hitbox of the attack as you fastfall meaning it'll hit all the way down: especially handy against shorter opponents
Tips? 10 of them no less?
Well, to save a wall of text, this video isn't unhelpful:
https://www.youtube.com/watch?v=UPU7GTemEXA
Though I'll add some things the video didn't cover...
* I say this all the time but the shield on palutena's arm gains hitbox eating abilities when you dash attack or back-air. Learn it and abuse it. You can dash attack through all kinds of things like wario's bike or people's projectiles and if you distance it right you can even dash attack through shulk's counter unharmed (if you do it from too far away the dash attack will end before the counter-blow comes out and the hitboxes on it will return) :3 Just be wary of dash attack's slow recovery.
* Jab is your friend. Palutena's jab not only has surprisingly high priority allowing you to stuff a number of attacks (e.g. diddy's face-hump) and projectiles, but if you jab then wait a small bit you can often follow up with a grab or another jab before the opponent lands and recovers (if you're too quick you'll trigger the jab combo so you'll need to practice if you want to get it out as quickly as possible :3 )
* Palutena's up-air is not only a great kill move but I honestly don't think anything can beat it from above while it's active. People's divekicks will get beat out by it so it's a fun thing to shove up greninja and ZSS when they're trying to dive down on you
* While the video pokes fun (deservedly so) at her default specials, they're not useless and worth learning to use if you're not playing custom. Auto-reticule in particular, if you can get used to its quirks, can shut down a lot of people's ranged game as it'll often blast their projectiles out of the air. Robin has a hellish time against it and even Samus will want to close distance to stop being pelted. You can punish a lot of things with it too fairly safely (it won't KO obviously but it'll help you build % and pisses people off an insane amount :3 ) Also auto-reticule can't be reflected back at you so feel free to spam it at reflector characters with impunity... just be wary of the slow startup and recovery
* If you're playing Palutena on for glory and your opponent is either fox or falco, toss out a reflector immediately as soon as the match starts. Not only will you usually wrack up a surprising amount of percent from reflecting their initial barrage at them before they realise what's happening but it helps set a "don't bother shooting" tone that will make them very cautious about using their lasers for the rest of the match :3
* If you're playing Palutena on for glory and your opponent is samus I can almost guarantee that all but the greenest of them will attempt a dash attack on you so unlike fox or falco, don't do a reflect at the beginning or you'll get an armoured shoulder to the face ^.^;
* I honestly wouldn't bother with her tilts in general until you're confident with the rest of her moves
* If you're not confident about hitting people with down-air when trying to catch someone returning to the stage, up-air makes a great kill alternative and neutral-air can often catch people. It'll suck them in if any of the spins touch them, lasts long enough to snag people who try to air dodge and you'll carry them down with you as you fall (shame the last hit knocks them back up again but it means they'll have to attempt to come back to the stage again :3 )
* If you fastfall up-air or neutral-air you can often end up dragging people down with you to the ground where you can catch them with a grab/jab to combo more.
* I suspect it's been fixed but I've not been on to try it: you used to be able to do short-hop neutral air while standing at the edge to edge-guard. Thing is, if you did it right you'd land and not do the last hit of neutral-air which for some reason turned the attack into a spike XD
Also, just to give you some ideas here's a recent palutena combo video someone made on wii-u:
https://www.youtube.com/watch?v=znWh98mlqtI
