Mix Your Own Color Palette
One of the many mistakes I made in my new enthusiasm for learning to paint with acrylics was not mixing my own color palette. I had to think back when I was taking private art lessons when I was 8 years old that we didn't actually start drawing/painting anything without seeing what our pastels would do when mixed. For some reason, I completely forgot (or ignored) this crucial step.
So when I realized I had skipped a step in my learning process I went out and bought disposable palette and an acrylic painting pad. I wrote down all my reds, yellows, blues, greens and browns on the inside cover of the acrylic pad, just in case I needed to replace any. At the top of each page, I wrote (for example) Cadmium Red Medium/Opaque/Single pigment, then spread a small dab of the color (with a painting knife) next to the name so I would know that was the color in its unmixed state. Then I skipped down and worked from left to right, and wrote w/Yellow Light Hansa or w/Chromium Oxide Green, and put the equal mixes of both paints underneath that. Then I would dilute with white twice (applying it to the canvas pad before further mixing). It was pretty amazing learning that red and blue don't always make violet (like Cadmium Red Medium and Phthalo Blue; go ahead and try it).
Now I know what each of my colors will do when mixed with any other. And you don't need to use that much paint, just small dabs.
It might seem like a "waste" of paint, or time ---but this will prove invaluable in the long run, as you'll always have your own unique color palette always at hand for your personal reference. And it's quite likely that the small "waste" of paint will save you paint over time since you won't be frustrated by trying to mix colors your palette's not capable of.