Sure! I can walk you through my general process! Sometimes I start with a design idea in mind beforehand and pick a gem that ‘feels right’ when i’m done, but that’s a fair bit more intuitive and harder to explain… so I’ll explain how I do the reverse, which is what I assume most people do too: pick a gem first and then making a design to fit!

Here’s one I made real quick! She’s not exactly perfect yet but I can show you step by step how I got her design through the first few stages!

(The rest under a cut to save space!)

1. Pick a stone you like! This can be either because you liked the name, or how the stone looks, or both. Whatever you like! There’s lots of sites out there that have databases full of gemstones that you can google and check out if you don’t know where to begin. Just make sure you’ve got a solid idea of the stone and colors that you wanna use. I picked Ametrine because I liked the name and colors!

2. Do a little bit of research and see what you can find about the stone. This can help you have a good place to start with the design if pictures of the stone itself doesn’t give you a jumping-off point already. As for Ametrine, I found that it’s associated with healing depression, and just making you feel good in general, among other things. I also made some notes about the kind of cuts and colors for ametrine that i was seeing in google image searches.

3. Start sketching out some ideas for how you want your gemsona to look! Since Ametrine is a ‘healing’ type of gem, I wanted a kinder and relaxed appearance, with a laid-back attitude. So I tried some of those ideas, and included some different poses too. It’s good to stay general here so that you can pick up more new ideas as you go along! 

Include some joke ideas too if you want, since this is the brainstorming stage and you don’t have to commit to anything. Sometimes the joke answers can lead to insight you might not have thought of before! For example, I like the ‘A’ in ‘Ametrine’, so I made one design full of ‘A’ shapes. I ended up liking that more than I thought I would!

4. Start combining your ideas and ading more detail. The ‘kind healer’ vibe I started out with sort of escalated into a nurse-like design, combined with those ‘A’ shapes I mentioned earlier.

Try to come up with a bunch of possible details to add. Similar to the brainstorming in step 3, you don’t have to commit to anything yet. Just keep drawing and you might be surprised what you come up with! 

If you need some guidelines, keep in mind what kinds of details that canon gems from Steven Universe have, and what kinds of things you like to see in a character design. There’s no specific rules for how to do this, but blending both canon ideas and your own can help you end up with a design you like. Remember; it’s your OC, so just have fun with it! 

5. Finally, just keep playing around with stuff until you end up with something you like! Add color only after you’ve got all your details figured out. As for coloring, try to limit your number of colors in your palette to 5 or 6 at the most. It keeps your character easy to look at! Also try to have 1 or 2 colors dominate- it looks much better when you balance a few main colors with other colors in small amounts for little details, like Ametrine’s pink dress and purple hair/body VS. the orange and white gloves/boots/ribbons I’ve added.

Try to divide up your colors so that you don’t have too many similar ones next to each other so you can break up the design and make things more interesting. For Ametrine, the main places that this happens are the ribbon-belt of her dress and her nurse hat. It’s also a good idea to repeat parts of the design in other places to bring everything together (the diamond/yellow parts in the hat and boots, the pink of the dress and the pink of the eyes, etc)

Also, don’t forget to put the gem somewhere and give them a weapon! I picked a scalpel because I like spear shapes and i thought the strong point would go with the point of Ametrine’s hair. Plus it’s medically themed! (Sorry for the lame weapon drawing; I’m still working on that lol)

6. Aaaaand now you’re done! Make a little backstory if you like: I imagine Ametrine as some sort of nurse on Homeworld that serves under White Diamond (who we haven’t seen yet, but boy isn’t it fun to think about characters we know nothing about? :D)

From here I’ll probably refine Ametrine a bit further but for now I hope that’s helpful to show how I make a gemsona from the ground up!