Just focus on the most basic of basic fundamental movements: the dash, the short hop, the fast fall. Knowing what you can do with those three movement options alone will open up a degree of control over your character that you might not know you had.
Smash is all about movement. Good movement will beat the most tech-heavy of opponents if they're not skilled enough in their fundamentals to utilize those options. I used to be the brainiac player of the group who put tech skill above all else, but my spacing was crap, my mindgames weren't developed, and I had no control of my character, despite knowing all of the techniques that I could perform with them, and being able to perform them as well. Until I learned to move myself around on the screen, I wasn't able to use what I knew to its fullest extent. Movement will allow you to use that tech, string those moves together in the most effective way possible, and position yourself in the safest manner you can.
In my opinion, it starts with just those three movement techniques; dashing, fast falling, and short hopping. Having control over those will allow you control over the options out of them, and so on, and so on.