The best advice I can give is to take time to sit back as much as you can and draw out matches. Not to be a **** or grief your opponent, and not to win either. Rather, at this point, where you are still trying to learn as much as you can and apply it, extending matches out as long as possible provides many benefits.
1.) You can observe your opponent more, see how they approach, and see how they apply things. This strategy evolves at higher levels into picking up on patterns, but it works at lower levels to see what works.
2.) You will develop a sense of control over your opponent by avoiding and playing this way. You won't win, and that's fine, but by making your opponent come at you, you are forcing them into a broad range of things that encompass "approaching." This evolves into mindgames and higher level control, but at this point, is useful for getting a sense of causing the game to go at your own pace.
3.) You are forced to react and predict attacks. If you don't want to die and get hit over and over, the best way is to, well, avoid getting hit. It's an old adage, but it applies to the learning process. It is vital at all levels to avoid as much damage as possible, and it paves the way to understanding positioning and spacing.
4.) On spacing: You will get a better sense for assessing threats at various positions. You don't shield when you're on the opposite side of the stage right? Well, unless Falco lasers are involved I guess. But usually it's a bad idea. The same applies for shielding outside of your opponent's range of threat. This range is not evident, because it is not based solely on the range of attacks. Rather, it is the range from which an opponent could reach out with their fastest attack from furthest away within your personal comfortable reaction time. If you have a slow reaction time, it's a further point away, and faster is closer, but it all is based on knowing that maximum distance. This can only be done if you spend time exploring this distance, which means keeping away. You will, over time, come to pick up on just how far away you can stay, and how much you can push into your opponent's range safely, by exploring this area of the game.
That's all I have to say on playing patiently, observantly, and defensively, but I do have another point of advice.
Play more, and play opponents who are honestly trying their hardest. If you do so with an observant mindset regarding what your opponent is doing, as well as taking notes on what you yourself are doing, what is working, what isn't, and what you can do different in every situation, you'll no doubt see improvement.
Another point:
DO NOT PLAY TO WIN
I can't say enough what a stupid mindset this is, because it's a paradox in the first place. If you aren't winning, you aren't playing to win, or at least, don't have the toolset and mentality to do so. So what do you do instead?
PLAY TO LEARN.
The more you lose and the more you learn from it, the better you will get. Don't play to lose by any means, but do play to improve.
Actually, **** it, play to lose a game once in a while too. Do literally everything you think will be the worst decision outside of outright killing yourself, then ingrain how many of them are genuinely bad decisions and how many of them serve as surprising gimmicks that throw off your opponent.
Finally, don't stop practicing your tech skill as well. High level play is a balance of thinking, outthinking, playing and outplaying, as well as executing on point, so keep in mind what you're doing, and hopefully get to a point where you are not consciously thinking how to execute, but rather thinking, "If I SHFFL a nair and drift back just a bit, it will poke out safely and make my opponent make a mistake in their attempt to punish."
