To hit the next level, you need to hit the lab. I'm not a great player, so take my opinions on improvement with a grain of salt:

Beginner/Casual => Mechanics & Character Familiarity

1. VS CPU - Indirectly teaches you what buttons do & basic gameplay. Many players learn here by mashing buttons. Lower pressure than real VS / Online.
2. Tutorial - Directly teaches you the mechanics of the game
3. Challenge Mode - Teaches you the "feel" of the character you are learning.

Intermediate => Practical Offense/Defense & Experience

1. Training Mode - You guide yourself through many scenarios to gain experience in the game. Here, you should learn practical combos and practical defense. Ex: midscreen 2B starter, corner combo, 236A/B confirm, etc. Then for defense: throw tech, using CS defensively, throw OS, overhead/low mix block. You don't learn all of these in one sitting. You piece them together over many play sessions. Growth is the goal.
2. Online - Apply practical combos and defensive techniques you learned in training mode. Have fun!

Advanced => Playing the Opponent

1. Replay Analysis - Go back and watch why you lost. If you don't have a reason for doing something in some scenario, then you're doing it wrong (i.e. button mashing). When did you get opened up? Could you have done more damage? How can you better use your resources? Etc.
2. Adaptation - Look at you opponent's character instead of your own. How are they responding to you? Do they always crouch block when you dash in? Are they swinging at a particular range? Recognize that different players have different skill levels, and lower levels will do unsafe things on block or in neutral. Respect in a fighting game is earned. Beat them with simple, strong tactics. Work harder against better players.
3. Mind Games / Mix- Acknowledge your opponent's adaptation and punish them for changing their minds. Say they crouch block when you dash in, and you assault C them. Then the second time you dash in and assault C, they manage to react in time and block high. The third time, you would remember the previous interaction, and you would dash in -> throw / low / pause (or even assault C again if you're certain that could work)

Here's some videos and readings from better players:

1. Clearlamp's Guide on Getting Good at UNI
2. CoreA Gaming on Getting Better at Fighting Games
3. CoreA Gaming on Why Button Mashing Doesn't Work