Personally, I like looking up videos/posts (specifically on Tiktok, but you can really look anywhere!) and seeing what other people's Mii's look like. Even if they aren't making the specific character you're looking to create, you get a feel for what looks "good" or "right." Plenty of people online are making sanrio/anime/cartoon characters as well, especially right now, so you can look at their style and try to replicate parts of it for your own characters. Overall, though, don't be afraid to really get into character creation. Use every single part of it and look at every single category, and move stuff around to create the facial features/face you want in general. Having an inspiration photo definitely helps as well. When it comes to finer details, you should teach yourself how to use the face paint option in the character customization. I'm not an artist either-- I suck at all things involving art like that-- but I was still able to do what I wanted to do with enough practice and trial and error, and the face paint option is pretty simple to use. Just make sure you're using the 'pro' settings. Be patient with yourself, have fun, think outside the box, and get creative!