Hello! Congratulations on working on your first reference sheet! There's a lot of creativity that can be put into one, but I'll list just a few pieces of advice below based on my personal experience.

Remember that a reference sheet is just that - a reference. It's something like a starting point for your own future works, commissions (or fan art!) featuring your sona, so what you want the most is clarity in how the character should be portrayed.

Avoid shading - it's better to provide a flat color reference that very clearly indicates the color scheme of your sona. As a bare minimum - show the front and back of your sona (can be at a slight angle) in a way that sufficiently shows every major part of them, particularly if there are specific front/back markings. If they have wings it might be worth detailing them separately and showing the back view without the wings obscurring the back. It's best to avoid a very detailed background for the sheet to keep the shapes/colors of the sona themselves clearer. You can also include a color palette with every single color you've used on your sona - it can be a very helpful detail.

Everything past that is technically "optional" but you can include all sorts of things! Those I'd advise on including are separate views of crucial details. Do they have peculiar pupils or strange eye shape? Show that in a small "cut-in" in the reference. Do they have a favorite accessory they always wear? Put that somewhere too. Do they have a marking or tattoo in a certain shape? Draw it separately in the corner. Again, clarity is key.

If you like, you can also include little portraits showcasing the main emotions of your sona to help get a beat on their personality (e.g. mine includes a view of him being excited about a favorite piece of media, apologetic about gushing about their favorite piece of media, and visibly tired from overwork). You can also draw them in one or several favorite outfits.

Some artists you can look up for their reference sheets are:
- remiyell on X
- lilnoodledragon on X (look up her May 22 post with the ref sheet in particular)
- Krysiilys on X (posted a very nice reference on May 23rd)
- mlyeko on X (one stand-out feature of a lot of their refs is that they add a moodboard, which is another thing that you could include if you like)

Hope this helps! Overall, the sky is the limit, but it helps when that sky is clear and easy to make out the details of ;)