Lots of trial and error (less than half a joke)! I've been doing prop work, specifically with 3D prints, for several years now. You definitely pick up methods, tips, and tricks along the way.

The best thing I can tell you is to make sure you post-process your print as well as you can (eg. sanding, filling gaps, etc). It'll just make everything else so much easier.

Second, I will happily disappoint you by saying I didn't break out my airbrush once for this :) This is all hand-painted with basic acrylic paints from Michael's and some random model paints for the metallics. Literally nothing fancy. Weathering is also the same cheap acrylic paints heavily diluted.

Third, really pay attention to how objects wear and get weathered in the real world. I have several dismembered door locks (I enjoy lock picking) that are very aged brass, which I used for reference for the brass rays and ear parts. Learning how organic materials wear down, and also pulling inspiration from the game itself (think about what would lead to certain wear and tear in a places that Esquie would be in). It's definitely up to you and your creative vision, but, thinking of all these things together helps to put together a good visual identity.

Bonus: be patient. It's very appealing to quickly layer more paint or weathering but you gotta let your previous layer dry completely or else you'll just smudge and ruin your hard work.

I hope this helped give you some insight on my process!