i'll give you the basics:
-side-b through shields (don't spam it, use it wisely)
-if you get a grab, dthrow pretty much everyone that isn't a fast faller and follow it up with a bair or uair depending on how they di. uthrow fast fallers.
-pop bairs and dairs oos.
-retreating shffld fairs are good in neutral
-edge guard with reverse uair. some characters like charizard and meta knight can just attack you and beat it out, in which case you'll have to space fairs and bairs or bait them.
-sometimes a good approach is to waveland into tilts or grabs. ganon is all about the mind games, so mix it up.
-after you do an aerial, double jumping and doing another one will sometimes trip up your opponent. like full hop dair to double jump dair works often against heavily grounded opponents.
good luck and have fun.