Well, you can either hope to enforce your game onto the opponent. Failing that, you need to know the match-up, otherwise your opponent has the edge over you, before the match has even started.
With 30 characters, it would be quite difficult to know all the match-ups. But one would essential learn the more common ones, as opposed to the more obscure ones. At my local arcade, I only have match-up knowledge of Ryu, Ken, Guile, Sagat, Yun, Fei. And when a completely new character comes in, like Ibuki - I really have no idea. But I’m glad I’m somewhat familiar with the Ryu match-up, cause that is almost like bread and butter, given how popular the poster boy is.
I think the only thing you can do, if you haven’t already sat down and studied all the the match-ups, or accumulated endless experience, is to read these forums for the match-up knowledge, or watch high level match-ups on your phone. Often they’re Japanese, but there’s a lot of great US players too.
If your gifted and clever, you could figure it out in the middle of the match. If you know your normals, have good footsies, spacing and zoning, then you could work out a solution. So for the rest of us, gotta do your homework.