[Ki-Mono]

Disclaimer: Keep in mind that people come in all shapes and sizes so all of these are general anatomy tips to help you out, but are not hard-and-fast rules

Side view:
Humans have the smallest hint of what you may call a "muzzle". With the nose, lips, and chin, extending from the rest of the face. I personally find it best to make the general shape of a face, and then branch the nose off of it. From there, simply make the shapes of the lips and chin underneath the nose. It won't go all the way back to the face. Instead, the lips will start to extend in the middle of the main nose area
Quarter view:
Although the nose will be primarily on one side of the face then the other, it is still in the "middle" of the face. So at a quarter view, the cheekbone on the other side of the nose should still be totally visible. The best advice I can give is a slightly lopsided triangle, with a circle in the middle. From there, you will add two smaller circles on either side. The farther smaller circle will be less visible for it is behind the nose.
The main part of the lips is right under the nose, with the whole of the mouth extending to roughly the middle of the eyes.
Then add the chin right under. A tip to help with size: try making the chin size the same as the lip size.

Both:
The eye will be placed right around where the nose begins to branch out. From a side view, it will be a small triangle. It seems you already have this concept down, which is great! I may just make the size a bit smaller. Brows will be placed slightly above, and then above that is the forehead.
Now, I notice the great lack of forehead in your drawings. This is a pretty common rookie mistake, so don't beat yourself up over it. But you need a forehead to start making your humans look less alien. In order to give you a visual on how big a forehead should be, hold your figures up right where your forehead is. You may notice that the length of your fingers is just about the exact same length from your eyebrows to your hairline. The hairline starts right near the ear, and slowly creeps forward on the head before becoming a pretty straight line (keep in mind this is a "straight-line" on a rounded surface).

Side:
The head needs to be slightly bigger in the back. We humans have quite large brains for our size, and it's more of an oval shape than a circle. Heres a visual for you. Notice how the head is more shaped like an egg then a circle?
As you go down, the neck will extend from the head, further back then the ear.
The neck is usually always weighted forward, and not straight up.
The jaw will go from the chin to the ear. Be sure to leave a little extra skin on the bottom of the chin area. We all have a little that hangs down there.
Quarter view:
I'd made the back of the head more visible, since, as we established, the head is an oval, not a circle. This in turn would make the ear more visible as well.
Cheekbone is right under the eye. Chin is right under the mouth. And jaw should line up to the ear. However, it needs to be more squared off.

I hope this helps! I'd love to see what you draw with these tips!

Refs: x x

[laika.]

Ah, thank you so much for the help! I've always hated giving characters foreheads due to my own self-confidence of having a large forehead. I've always been totally clueless on how to do everything under a nose, so thank you!

This was super helpful, and I can't thank you enough for both a large written piece and visual help!

[Ki-Mono]

Ah, thank you so much for the help! I've always hated giving characters foreheads due to my own self-confidence of having a large forehead. I've always been totally clueless on how to do everything under a nose, so thank you!

This was super helpful, and I can't thank you enough for both a large written piece and visual help!

No problem!
And yeah, foreheads are still the bane of my existence too. As I always say: practice and reference images are your best friend.
The only way to get better at the beast is to practice those dreaded foreheads!