There's a hands-on educational program called Syntorial that introduces you step-by-step to all the features of a typical subtractive synth using just your ear.

There's a hands-on educational program called Syntorial that introduces you step-by-step to all the features of a typical subtractive synth using just your ear. On every step, you listen to a sound producible with the features you've unlocked so far and recreate what you hear, then it tells you which parameters weren't quite right so you learn what to listen for to hone your ear. Subtractive synthesis is different from wavetable synthesis, but most of the concepts transfer. And Syntorial even has a free download (after the initial purchase) which covers Serum specifically, as well as a couple other industry standard synths. It might be pricey depending on how invested you are in learning, but they have a demo so you can see what you're in for. From my perspective, outside messing around by yourself, I don't know of a more cost-effective way to learn everything that it covers, and it saves significant time over messing around.