A pretty big thing missing from Serum that me and a friend noticed recently was that there is no stereo white noise in the noise generator. Since the noise generator in Serum is only a resampler, the only workaround I found for it was to generate my own stereo white noise, bounce it into wav, and place it inside Serum's source folder where all the noise files were. If anyone knows a better way to create stereo noise in Serum's noise generator, I'd love to know. But so far this is the only way I know of.

One cool function I love about Serum is it's ability to do AM / FM modulation using one of the Wavetable's as its source. This opens a ridiculous amount of possibilites since Serum let's you draw in your own wavetables. Seamless did a video about it here if you want to learn more: https://www.youtube.com/watch?v=2DdinGepls4

Also... not really a tip or trick but check out the Reverb filter. No idea what it does but holy fuck is it insane.