I’m a new player who is trying to learn the game with Ryu at the moment and my biggest problem in my opinion is that my inputs simply are not coming out half the time. I’m using the pad which isn’t necessarily how I want to play in the future, but is the only option atm so I’m making do; however, what has been the most frustrating thing as I mentioned is the failure of my inputs. The fireballs come out only about half the time and the Shoryuken motion is driving me nuts. I can’t do it on command. Usually, the SRK comes out when I don’t want it, usually when I’m trying to throw a fireball. Any tips?
Just make sure you are ending your fireballs at forward and your shoryukens at down-forward,I would recommend just going to training and practicing the motions a lot daily,eventually muscle memory will take it over in matches 
I also had the same prob. Just practice in training mode. 
One small thing that helps with regard to fireballs is just consciously waiting a little. I found that my problems often came from the fact that I just pressed punch way, way too early.
Partly echoing the previous posts, go into training mode and turn inputs on. Make sure you’re pressing punch at the end of the quarter circle forward motion (you can check if you’re doing it right with the inputs displayed). Also, you can only have one fireball on the screen at a time.
battles much with keyboards