The best way to improve is to play consistently, play people who are better than you whenever possible, seek criticism within reason, learning from other players and videos whether that be on YouTube or Twitch, and just have fun.
I’m going to have to disagree with the notion that Smash 4 doesn’t teach you how to play, or that players shouldn’t practice and just wait for Ultimate. But I’ll address the first part about the game not teaching you how to play.
That is a polarizing mentality, especially since the games from Brawl moving forward have functioned the same fundamentally, but the implication that the game should be teaching you how to play means that you are reliant on playing the game mechanically, as opposed to mentally. Yes, some of Smash 4’s mechanics are sketchy, like DI deduction, knock back functioning very strangely for some moves, down throw to up air being everyone’s combo starter. These things leave a lot to be desired, but the good players remain consistent from each smash iteration because there is less of an emphasis of playing smash at a technical level and more on a mental level: mind games, baits, momentum, reads, option selecting, tournament nerves, etc. Simply by playing smash and trying to build upon your foundation you will do well.
There are two types of players I see in tournaments. The ones who are in top 32/16/8 consistently, and the ones that enter more than the top players but still go 0-2 in bracket. Odds are these players don’t emphasize understanding opposing players, get frustrated at their performance, leave bitter, don’t try to understand what they could have changed, and talk to their other members of the 0-2 crew. This is due to not using their experiences wisely or seeking peers to connect with. It can honestly even be as simple as making friends with players. Players in the NBA and NFL often hang out with their team mates to build rapport, practice, build upon each others understanding. This creates synergy and helps both players improve. Nothing is created in a vaccume after all.
Either way, you should attend smash fests, tournaments, and yeah play for glory. People are bashing it by saying players aren’t good, but I’ve seen people who say that get bopped because they don’t know how to play against inexperienced players or can’t punish properly and just do a fancier version of what the “lesser” player is doing. You may find some good people, you may find some bad, but if you can play against both adequately, then you’re improving. You don’t always have to stunt, just try to win first lol.
Good luck. Keep playing!