Spamming buttons is not really bad tbh.
But you can always see the "Spell is not ready" text in the top of your screen.. ^^
I'm not sure what you are playing(pve/pvp) but when I first started I was like "Ok, I gotta know the GCD in my head so I don't press to early", so basically I pressed the button once.
But now, if you don't already know you can load another cast(as a caster dps/healer) while the first cast are already going.
So it's good to spam.