well peach's main weakness is that her movement is slow, as her ground speed is atrocious, and her falling speed is quite small. her floatiness makes her die very early off the top too, so picking big, wide open stages with high cielings (aka dreamland) is very advantageous for peach. despite her slow movement, her approach game is actually quite good. her turnips are an excellent tool, and provide her with glide tossing and aerial glide tossing to enhance her movement. they bounce of people so that you can jump up and regrab them for quick use as well. if you float with her, start an aerial, then land duing the aerial, you lose all lag, and suffor only 4 frames of landing (making this the most efficient means of reducing lag in the game). because of this, you can approach with her nicely ranged fair (or even a dair) from above, hit someones shield, and almost instantly jab or dsmash to stay entirely safe and pressure on shield. similar approaches can be done with bair or nair low to the ground. CCing with peach is great because her dsmash is so fast, will clank with almost everything, and actually does more damamge to people if they try to CC (does a full 60% i believe if they try to CC since all hits will connect). all of her tilts, uair, and up throw/dthrow are great combo tools. she usually finishes with edge guarding since her recovery is so amazing, and using float she can hover by the ledge or travel wayy offstage to gimp. she can also finish with her powerful forward throw, her dsmash, an fsmash (usually the golf club, but the pan works on floaties, and the racket on fast fallers). if you want to get fancy, try setting up a tech chase with dthrow and finishing with a DACUS, since her upsmash is so powerful (just hard to land).
overall, though, i recommend watching videos of peach to see how all of this connects together. armadas melee peach is amazing to watch, and people like vanz, nintendude, silly kyle, and white peach all are other that have videos on youtube and will be able to demonstrate a lot of good techniques with her.
