First off, peach has the worst wavedash in the game. this does not mean you shouldn't use it, it just has the generic uses of a wavedash, the generic uses being spacing, mindgames and more. Wavedashing is used normally to grab the ledge with most characters, but some have other ways.
Bowser: Up B off ledge to grab
Link: Run to very edge of stage and press up B. If done right you should perform your up B and grab the ledge out of it.
Sheik Same as link, direct yourself away from the ledge, and then when the explosion is about to happen, towards and you will grab it.
Peach: Float Backwards
Bowser's and Peach' you will use most of the time, Link's and Sheik's are flashy. Other characters can do it as well, I just named a few. Most other characters wavedash backwards while facing away from the ledge.
The reason you will be grabbing the ledge is edge hogging, your opponent is using their up b or whatever to get back to the stage, and have to grab the ledge. You use whatever meaneuver you have to grab it first, and they can't grab the ledge since you are on, thus making them die. It is more useful than it may sound right now.
And here's the wavedashing chart. From greatest to least
Luigi
Ice Climbers
Mewtwo
Marth
Yoshi
Roy
Ness
Mario/Game & Watch/Doctor Mario
Samus
I think that's the first part.And then the worst wavedashers
Link
Zelda/Peach=worst
You can tell if a character has a bad wavedash if they don't seem to slide after the wavedash.
Sorry for all that random info but...
L canceling: When you are performing an aerial move (B button moves dont count) press L or R all the way down when you hit the ground, or just a little before and you will have 1/2 the landing lag. Lag is how much time it takes until you can move again or use an attack, etc. You really need L canceling with every character. Always L cancel. Just ask everyone else how important it is.
Float Canceling: Peach has something even better than L canceling. Float canceling. It is a glitch. In the air when you are about to perform an aerial, float, and perform an aerial. Stop floating as soon as you want , or dont for a while, as long as you hit the ground while still performing an aerial. If done right, you will have 4 frames or landing lag. 1 frame =1/60 of a second! A normal L canceled aerial will probably be around 13 frames. It really makes a difference.
And abuse them turnips. Hope that helps
And if you need anymore help, you can private message me.
EDIT: Oh that other guy beat me to float cancceling. Here is a video completely explaining how float canceling works:
http://youtube.com/watch?v=uCi5sLn0Bcg