This. I have the same problem when I jump into a new fighting game, so i usually play the slowest character. This forces me to think before I act and also allows me to observe how others use the faster characters.
Also, go into training mode with the character you want, and find some sort of strategy or combo that might be useful and memorize it. The combo may or may not be effective against real opponents, but it will force you to learn something other than mashing. Once you get past the button mashing thing, you can delve deeper into the game mechanics and really understand how things work.