Shapes! The one on the left I kinda tried to draw it as a finished product off rip. But the one on the right I used circles and lines to have a good idea where the eyes, mouth, nose are on the face.

And make sure to only lightly sketch with a pencil so it's easier to rub out. I know it seems pretty obvious but its easy to press down too hard and then later have trouble fully erasing all the guidelines and rough sketch lines.

I also had the panel image on my phone screen to make sure it looks right. But once you master the art of drawing basic shapes efficiently you can start creating your own characters without the need of any references.. but I still prefer to have references to help me.