Eyes are actually a thing i struggle myself so here is a little tip i always do that keeps me somewhat afloat.

The key of making a eye nice (cartoon or not) is to make it organic, that means that if the character appears in real life their eyes work properly and not fall off, have twisted eyesight or something.

Again i need to stress the fact that referencing from real life is very important to learn about eye shapes. Nothing better than the source material!