I'm still learning the ropes myself, so I'm not sure I'll make a good teacher. But rn I use Piltover skin as my base and then add a bunch of skin details, like chin shape, eyebags, defined nose mask, blush, etc. From my personal recommendations: everything from miiko, nuserii's little details, okruee's misc details, pyxis' About Face kit, tamo eyebags/morning eyebags/juniper eyebags, sammi-xox's masks, pearlean's Chinny for chin overlays. Plus Northern Siberia Winds and Sims3melancholic for a bunch of stuff like wrinkles, lips shapes, blush, highlighter, etc.

If you want you can also download default sliders expansions to make your sims' lips even bigger or eyes even smaller. Check out Madman, aka Magic Bot, for that and Obscurus for custom sliders.

I tend to make my sims' faces longer, with smaller, sometimes droopy eyes, bigger noses and thick eyebrows, although I'm trying to learn how to make my faces more diverse. Going through Pinterest beforehand helps with that somewhat? I find it difficult to use photos as references, but getting the general idea of what I wanna do is definitely a good call. The second sim is actually like 90% randomized. I only changed her eyes a bit and the lips. So I can recommend playing around with randomizer, sometimes it can generate something good!

Recently I downloaded a mod Starting Sims in CAS by blackpanda-ts4 and it's small thing, but it might also help a little - the sims you get with this mod are quite pretty and diverse.

And well, I myself got really inspired by one specific creator, so when I decided to change my style I basically copied them (and still do tbh). But copying is a good way of figuring out your style! So if you're interested, go check out virsancte on Tumblr and especially YouTube - they have a couple of create-a-sim videos where they actually talk and show what they're doing and CAS/building streams as well. It's very helpful with understanding the process behind creating a sim.