Ok, so as many of you have expressed quite strongly before in the comments, you're having trouble with eyes
Either you can't get them to look the same, they take up the entire face, or you're having difficulty conveying expression.
Don't worry! I've got you.

Ok, so just to start. To the people that practice eyes by drawing one eye and only one eye...
No. Stop.
That is literally one of the worst ideas I've ever heard. And I've seen incest.

I know that your teacher may say to draw one eye at a time, but it'll end up making things much more frustrating for you when copying over to the other eye. ESPECIALLY when doing realistic eyes.

Ehem... Anyway. Let's get started.

Drawing eyes is just like pregnancy! It starts with a plus!

Make sure you draw lightly when sketching the facial features. This way you won't see any marks on the face after you ink it and erase it. (Considering the face is where they're most likely to show.)
But of corse, I have a lead hand, so it's hard to take my own advice.

The plus will help you centre your eyes for practice, a friend once taught me a trick, and I'm gonna teach it to you.

Adults eyes go above the line.

Teenager's eyes go on the line.

Children's eyes go below the line.

Now, of corse, there are many different eye shapes to choose from, depending on your style, the character, and overall aesthetic appeal.

I personally like using smaller eyes and circular irises usually with no pupils to give my style a more realistic/sassy look.

For children I make the eyes more cartoonish and give them larger circular iris' and no pupils. I like adding hash marks to the pupils.
(I add hashmarks to everything.)
(Really. All of my lineart shading is hashmarks.)

Most artists I've talked to don't really care for the one eye rule. I use it a lot of times.
(Because I love anatomy.)

Moving onto expression. The face is usually a key factor in determining what your character is feeling along with body language.
I'm going to do an ENTIRE chapter on expression and body language, but for now..
Generally the rounder the top of your eyes are the more positive the expression/vibe they'll give off will be.

Larger iris' usually translate as "cute" or more childish. But in some cases they can be downright creepy.

The more pointed the sides of the eyes are the more "feminine" they'll look.
(It gives off kind of a cat eye)

Just remember to draw the top of the eye first, then the iris, then if you do the bottom of the eye, do it.

Eyes can give off a lot about your character from the first moment the reader lays their eyes on them. Personality, age, many things can be determined by eyes alone. Which is why I feel like it's my duty to good full head and ham perfectionist when doing eyes. I have to get the right eye shape for my characters or else it drives me crazy.

I mean common, you wouldn't give Widowmaker cute friendly eyes, neither would you do so for batman, or any serious character.
Eyeshape is important. Oh, and one other thing I forgot to mention.

WHERE IS YOUR CHARACTER LOOKING???

Seriously, this is the BIGGEST pet peeve of mine.
If you can't tell me where your character is looking, or you tell me and in reality their staring off into the void of space, HUSTON WE HAVE A PROBLEM!
I've seen SOOOO much fanart like this and it bugs me. It bugs me so much.

Character is looking directly forward, the pupil is in the middle of the eye, and usually some what cut off.
To the side? TO THE SIDE.
Down the left, DOWN TO THE LEFT.

Please just save me from this toture!

For characters with masks, many people will actually slightly contort the mask to show expression.
For example, making the eye sockets of the mask widen in surprise, or exaggerating the head turn.
If your into Undertale, you can see people do this with Sans all the time.
Bone can't move and bend. But we contort it so we can show expression.
For character's with pitch black eyes head positioning is REALLY important.

Again, IF I CAN'T TELL WHERE YOUR CHARACTER IS LOOKING WE HAVE A PROBLEM!

And I see even incredible and amazing artists making this mistake and it bugs me! I want to scream!!
Practice with iris positioning, experiment with expressions. Exaggerate things.
I have never drawn perfect eyes on the first attempt. It takes me two to five times to get them the way I want. Maybe you can even make a little eye expression chart for yourself?
I'm not feeling to great while writing this, so sorry I'm not going super in depth.
Eyes are hard since everyone has a different style/approach to them.
Just do whatever you feel comfortable with.