Some things I have done to improve my efficiency is customise my Inkscape interface, by that I mean I removed all the unnecessary open windows and bars. You can see that in my screenshot. I have also customised the keyboard shortcuts, so my most used keys are WASD and surrounding keys (gamer here so these keys are most familiar when using both keyboard and mouse at the same time).
Alongside this, I have also created keyboard macros for some certain tasks because I couldn't change all the shortcuts. My keyboard also as separate macro keys in easy to access locations. So I have added stuff like delete, group, merge, split, and a couple others to keyboard macros.
As for more complex stuff, for my vectors I do the exact same process as everything else, but you are essentially just adding more paths to the image. I have slightly changed my process from this tutorial, but those are little tricks I've just picked up as I play around with stuff. That generally happens over time when you discover new stuff.
OCs are a completely different story since you will be creating them from scratch and not tracing over an existing image. I haven't had any experience doing this, so I can't really help there.
Some general tips I can't stress enough, the less nodes you are, the smoother your image will look. So try finding the best places to put your nodes to create the curve needed.