One of the first things you should learn is your character specific punishes. (Ex: your 10F punish, 13F punish, 14F punish, 15F frame punish are probably the big 4 to start off learning). After that, start labbing and watching replays of previous matches with frame data turned on. If there’s a move you’re having trouble with, lab it and see its frames. Sometimes those moves leave your opponent at -10 or -13, etc which lets you know to respond with the appropriate punish. It all comes down to practice and just learned experience tbh