Two things I'd emphasize. First, don't underestimate the fundamentals of hand position (your finger should be curved a certain way, you can see my hands in the video as an example.) Scales and other such exercises are important for getting accustomed to moving your fingers across the keyboard in such a way as to avoid stopping and readjusting yourself. For more complex songs down the line, you have to be able to move your fingers in certain ways, like crossing them over each other. I'm at the point where all that is muscle memory, but it has to be built up. Second is less about technique and more about where to go once you have that down. I've found that it's good to learn the relationships between chords. That allows you to improvise parts that still sound like they fit the song (putting your own spin on it.)
