Hi! I use Serum to make not only all my bass sounds, but pretty much everything outside of basses as well. If I had any tips for bass design within Serum in particular, they would be as follows:

1. Make good use of FMing. Serum has an 'FM' feature that can be really useful in getting you nice sounding and commonly heard basses. To start out, try FMing some basic shapes. You can set oscillator 1 to FM mode by clicking on "off" and choosing "FM from B" (make sure to turn oscillator B's level all the way down). Generic sounding basses can be made by FMing a really low oscillator with a really high one (in terms of octaves).

2. Use modulation to your advantage. Common parameters to modulate include filter cutoffs, levels and wavetable positions (certainly when using complex wavetables, for the last one). However, why not try modulating FX parameters, such as phaser depth, dimension mix and distortion? It's good practice to learn what each effect does to a sound, and if you're feeling confident, maybe go more in depth and learn what changing each individual parameter/knob does. By doing this, you will get an idea of what you want to modulate and by how much. I usually modulate the FM value a small amount and growls often have the pitch automated, as well.

3. Use effects outside of your bass patch to bring out its true potential. Add stuff like saturators, compression, multiband compression, waveshaping, multiple subtle distortion effects, reverb, haas-effect delay etc. to your bass channel's effects section to sharpen it up and increase the perceived loudness (amongst other things). Don't go overboard with distortion, though, as you probably don't want to just blast the listener with noise and clipping bass/sub.

4. Once/if you have a bass sound you're happy with, try duplicating it and changing the shape and/or speed of the LFOs and other modulators. This way you can get even more out of a good bass sound, and maybe even turn it into something different.

I'm sure there's a lot more I could add, but I don't want to put too much down since I don't know whether you use Serum. Much of what I've said is more or less 'universal' though, so to speak, as it can be applied to many other synths. I hope this has helped, and have lovely rest of your day.