I helped someone out with a similar issue, so I’ll just copy my answer:
As you continue to play the game, you’ll find that it’s more important to focus on your opponent rather than yourself. You should already have an idea of the stage layout and your character’s moves and traits; now inspect what your opponent is doing. Max concentration is achieved when you’re zooming in on one character only. You’ll have much better chances to react to their movements without getting distracted by your own; think methodically and go with their flow.
If they dash dance, prepare for multiple outcomes. A bad guess is good, because your opponent will know that you are aware of a move that may be beneficial to you in the matchup. You can make them stop doing stupid things this way; if you used a move that’s good against jumpers, for instance, they’ll have a tendency to jump less, giving you a smaller number of options to deal with. If they don’t learn that you can predict them, however, it’s likely they’re not thinking straight.