Can i get good by fighting NPCs?

If you're at a point where you can beat the AI on nightmare then I don't think the single player content has anything left to teach you. You'll plateau unless you play other people.

AkahanaKatsu said:

I get that losing is the best way to learn, but how am I learning when I never even get the chance to move my character?

Every time you lose try to figure out something you could have done differently. Say you have a game where you immediately get hit at the start of the round then get reset to death. Ask some questions. Why'd you get hit right at the start of the round? What were you doing? What were they doing? When you got reset, what kinds of resets were they doing? Could they be blocked on reaction? If not, are there certain guesses that give you a more favorable outcome than others? Set it up in training mode and figure out what your options are.

The main reason people will tell you not to do that is that it creates bad habits(somethings that work on computers won't work on players.)
I recommend playing against random people, finding someone of similar level, then befriending them and playing against them repeatedly.

The forum has a beginner match finding thread so you could try poking around there for some people to play.
NPCs I think are only really good for learning your characters move and the basics of the game. Once you've learnt the basics they can be good for practising tech and combos in a more pressured situation tha n training mode but they are otherwise a bit redundant in my mind.
You're definitely better off learning by playing people. What I did when I was first learning is I'd add people who were anywhere near my level of skill (and a few who were way better) who I then asked for advice and played games. I personally like to play characters I know less about when playing new players so some more skilled players may do that as well.

I find that fighting the AI is only helpful for the following:
- Practicing combos on moving opponents
- Practicing conversions
- Basic Defense

Other than that I would say that trying to learn from fighting the AI is actually detrimental; it may make you develop bad habits, think things that are actually effective against humans are ineffectual, or that ineffective strategies are good, etc.

On losing, try not to think of it as losing.
Try watching higher-level players and see what it is that they do that works but also look at why they or their opponent are losing and getting hit. Analyse the match, don't just look at the fancy exciting bits and go "I wanna do that."
Afterwards go on a match and don't consciously think of the matches you've watched, instead keep what you've learned at the back of you mind and it should come to you naturally. As you play, don't watch the match as a player, rather, approach it similarly to how you watched those match videos.

Then again, this is my own particular way of approaching things so it might not be for you~