Siberian, what Pryde and C.Falcon are saying is true. Looking at the games you play based on that list, and based on the fact that you all don’t play SF as a main…I’d say your main problem is the metagame. And if you don’t know what that is, in a nutshell metagame is what you’ll be doing when you or your opponent isn’t performing a combo. That’s where knowledge of normals, character matchups etc. come into play.
Pryde’s suggestion of watching YT vids is very good. You can see other players’ metagame, and how they adapt to their opponents - and how they make their opponents adapt to them. C.Falcon’s suggestion is a good one too. You MUST learn basics before you learn advanced anything – this should go without saying. It’s possible, however, to have played fighting games for X amount of years and not have basics down. This can range from doing a simple jump-in combo into a special or a command for a super. Or, in your case, not knowing when to attack, or how/when to do a combo against a human opponent.
My advice for you is to get in A LOT of match experience, but only after mastering the basics in whatever game you’re playing. You need to establish basics first, then though situations and so many matches, things will hopefully start to fall into place. Why am I telling you to master the basics? Because Melty Blood, Rumble Fish, and Akatsuki Blitzkampf play ENTIRELY DIFFERENT from Guilty Gear, KoF and Street Fighter. Although fighting game experience carries over, every fighting game has its own set of basics to its system.
I didn’t include Arcana Heart in my example because it’s in it’s own level of awesome (shameless bias)
EDIT: Phoenix already said a little of what I was going to say lol