There's a local player that abuses the shit out of CC/shieldgrabs. He has a method that I call dan grabbing (lol).
You can't buffer a grab but you can spam inputs by
(holding down if CC grabbing +) L + mashing A with your thumb and Z with your index finger quickly.
Implementing this has made a noticeable difference in my grab game.
In line with this, in some situations I like to err on the side of early and double tap an input as quickly as possible. This allows me a weighted ratio of early inputs to some slightly later than possible but still passable (obviously worse than practicing consistent early timing). I also mash the C stick from slightly above horizontal to slightly below and back again when I want fair out of hitstun etc.