Can't speak specifically about SF games but as far as general improvement goes, the main principle is that improvement and victory are unrelated. Sure, if you improve, you will also win, but it isn't that simple. See, if you improve, but not as much as you need to win, you will still lose, while having improved.
Fighters are beautiful because there is no skill ceiling, not for you, but not for your foes either. Hence, your paltry improvement has to keep up with and surpass the improvement others are achieving. That is an immeasurable challenge and not one that can be overcome with a single piece of advice or a single tactic. It's kinda like when an 80 year old master wipes the floor with much more athletic but young kendo fighters. Unless you also amass that much experience, you will not win.
So, in simple terms, playtime. Do you think it fair someone with 5000 hours on the game would lose against someone with 500? No, that would not be fair. Doesn't mean the latter person sucks, just that the former is JUST THAT GOOD (yes in caps

). The only thing you can do to stand next to that person is climb the playtime mountain. Just because they're still way above you, doesn't mean you're stationary, it just means you still have a long way to go, while having fun and improving.