There's really nothing you can do to prepare in a few mere days.
But, first of all, dear god, projectors are laggy as heck. Don't use them. Unless it doesn't bother you, which probably isn't likely. If is any option for a television, I advise you to use that. Don't forget to put it on Game Mode.
In general? Watch your opponent spamming things all the time. That's really how a lot of non-competitors win, and it is VERY exploitable.
Ganon spamming side B and the unavoidable down tilt? Roll or spotdodge on reaction, and attack them back. Or, you could run away with some fast character and dash attack them.
Character spamming projectiles? Roll through them, jump over them, or even fire projectiles back! Spamming roll after you approach them? Time it right so that you can attack them in between their roll spamming. Or, using a projectile that's generally as fast as their rolling, e.g. Pikachu's Thunderjolt, or, use an attack that hurts people with a long duration, e.g. Toon Link's Boomerang. DON'T use jab though... dear god. You need to stay safe as well, and people can still react quickly out of rolls, and in Smash 4, jab has a really long animation.
Anyway. Watch out for patterns, and figure out how to beat them using the tools that your character has. Think clearly, don't panic.
