Find a training partner to play against in person is the best way. Until then, focus on movement and execution.
That said, just go to an event and play people. No matter when you start going to events and no matter how much practice you put in beforehand, you are extremely likely to got bodied. And that's 100% okay. Pretty much everyone has gone through that same experience. It doesn't have to be a tournament. A simple smashfest near you is perfect for this. You'll lose most/every game at first, but you'll be able to talk to the people beating you and get advice so you'll improve much faster.
Just go in with an "I'm new but looking to practice and learn" mentality. Most smashers I've met are pretty receptive to that attitude.