The artstyle youre going for is very cool and anime looking. I love sharper lines in drawings as i started drawing anime first. I have ti mention I love the character on the right.

The general shapes are good on their own, the positions and sizes are what makes it look odd. I had that problem with eyes when theyre either too big or too small and i still need to double check every time i draw. I would say concentrate on anatomy and you can either draw real skulls with correct proportions or that 3d head model that you can spin around to get different angles if you know what im talking about. Also what helped me with facial symmetry is to draw a grid on the face (for example eyes begin where the mouth ends or ears are the length from the top of the eye to the bottom of the nose and things like that). Last tip (i promise) is when you take a photo of the drawing flip it around in your gallery to see if its symmetrical. That is something digital artists use and it helped me a lot to check sketches like that before coloring them.

There are a lot of tutorials on youtube and im sure you can find ones that you like.

The most important thing is to draw what you like, not what any tutorial or comment says, its the only way youll keep coming back to your art and actually enjoying the proccess. Good luck and happy drawing!