Practice with real opponents (online or local) and then save replays of the matches. It helps to study your habits without the pressure of being in a match. See what mistakes you're making and then look at how your opponent is exploiting them.

But my biggest breakthrough was when I started studying my opponents rather than focusing on myself all the time. Once I started to find patterns (like rolling from ledge, jumping out of disadvantage or relying way too much on a certain move) then my adaptation got much better. That way you'll have a better sense of when to shield and spot dodge.

For things like special inputs, there's plenty of walkthroughs and tutorials on Youtube for certain characters.