Uhhh I'll be honest I've only done this once lol. I'll try to answer your question but I don't have much personal experience to draw from, and even then it was my partner at the time who asked me about my kinks first, so it seemed natural to show him my art at the time as well.

If I had to do it again, personally it would be when we're more comfortable knowing each other intimately and I would bring it up during a discussion of the things that get us going. I wouldn't show it to them at first, but I would talk about it, explain what I enjoy about my fetishes if they wanted to know more, then mention that I enjoy drawing it for fun. Only after that I would offer to show it to them if they were interested. Hopefully they'd be understanding even if it isn't something that appeals to them.

I think it's much healthier to air out this kind of thing instead of feeling ashamed about it. I'd never be able to hide this part of myself from my partner, at the very least I'd need their acceptance that I'm going to be drawing kinky shit for the foreseeable future!