WD is useful OoS when you would intuitively roll, after every kind of jumpcancel where you want to stay grounded (waveshine as Fox: Shine -> WD)
Watch some Melee videos first because that is the fundament PM Fox builds on.
As Brawl player, you are probably familiar to RAR, this is the most important thing Fox has gained over the transition from Melee to PM.
Fox is a very technical character so here are the things I would try to test your current technical level and improving it (a little bit sorted by difficulty):
short hop; L-cancel; wavedash; short hop laser; wavedash OoS; tomahawk (short hop->fastfall land without any move) into grab; Different up-b angles (get used to sweetspotting from above, high angles to reach platforms etc.); Roll->shine & spot dodge-> shine (you don't want to roll or spot dodge that often but if you do, the shine is your best bet to protect you afterwards); SHFFL aerials (short hop -> fastfall -> aerial ->L-cancel or short hop->aerial->fastfall->L-cancel depending on timing); RAR bair (practice mostly in ledge situations because it is mostly used for edgeguarding); Up-smash OoS (jumpcancel -> up-smash); Up-throw->Up-air combo; Cactus dashing (dashing towards an opponent-> (shield shortly if you think they will attack ->) WDing back -> repeat until you get a grab); RARWD (a wavedash after a rar, the result should be a wavedash in your original direction while now facing the opposing direction, great for getting the ledge); side-b from the ledge (drop drom the ledge ASAP, jump immediately, side-b as soon as you are at stage height and you will have ledge invincibility on the first part of the move); WD onstage (drop drom the ledge ASAP, jump immediately, WD onwards, now you can do a grab/up-smash because if you did it correctly you will still have invincibility); shorten illusion (if you press b while travelling with side-b again, you shorten the illusion, frames 21-26 iirc); nairshines&drillshines (SHFFL nair/dair -> shine -> jumpcancel ->repeat); short hop double laser; Firestall (drop from the ledge ASAP, jump immediately, up-b so you are directly next to the ledge, you will automatically regrab if performed correctly); shine OoS (jump->shine on first airbourne frame); waveshine (WD after shine); waveshine OoS (Shine OoS -> WD); Shinegrab (shine -> jumpcancel ->immediately grab); doubleshine (shine->jumpcancel->shine, then mostly WD or SHFFL aerial); waveshine -> followup (into grab, up-smash etc.); Westballz pressure (like a doubleshine->WD but you do the second shine when slightly in the air so the next jump will not have to go through jumpsquat frames); Shinegrab OOS (Shine OoS->jumpcancel->grab); multiple waveshines; multishining (repeat doubleshines principle multiple times)
Feel free to ask more questions, I will try to answer them as good as I can.