Step 1: Crush any ego NOW. If you don’t, someone else will do it for you.
I started playing 2D fighters in '06 & started 3S in '07. Unlike you, I didn’t have any foundation for fighters. You at least have some fundamentals from playing SFIV. Be thankful for that and start there. Use what you know, but always go into a match looking for something new and DON’T FORGET IT. This game will teach you a WHOLE OTHER LEVEL OF MIX-UP.
Step 2: Don’t get discouraged.
Thank you for posting your first response the way you did. Expect to lose, but expect to learn something from losses. I’ve gone 0 - 50+ on people when I started. If you get frustrated, take a break and THINK it out. This, out of all games, will force you out of “auto-pilot.” Muscle memory can sometimes work against you. You need to get in the habit of “confirming.”
Step 3: Play people who kick your ass.
Universal tactic for getting better in any sport. Yes. 3S is a sport. For some, it’s the oxygen to their breathing. I’m not recommending you to flop your college final for playing 3S, but dedication is required if you want to become at least “competitive.”
Step IV: Forget theory mindsets like “The best pattern” or “The best poke”
No more auto-pilot. The “best 3S players” have a style, but each player is definitely scrutinizing their contemporaries in trying to find “alternatives” for certain “situations.” In 3S, it is paramount that you know as many different things that you can do in any situation as you possibly can. 3S gods are known for punishing any pattern that you develop (whether or not you even know you’ve fallen into a pattern.)
Step 5: Develop your “yomi”
Search forums for the definition of “yomi” in the competitive context.
Good luck with learning 3S. If KOF fighters can win SBO '09 in SSFIV, then SFIV players can evolve into 3S players. (I had to take a shot at SFIV players getting beat by KOF players. I think KOF was more difficult than SFIV at that time.)
Advice I got when I was still learning basic fighting game fundamentals: “Mix-up EVERYTHING. Change your timing on when you let your jump in hit. Change when you dash. Mix-in more throws. Mix-up throw set ups . . . etc.” [You get the point.]