In order to make your eyes look bigger like mila kunis, there are two ways for you to do. First of all, you could do the makeup on the eyes part to make them look bigger by using the eye shadow and other things. Then you could wear the colored contact lenses which will also make the eyes look big and beautiful.
From what you said, I can see that you like mila very much. As far as I am concerned, I am quite into her too, for her role in Friends with Benefits. Anyway, you should know she's got a pair of big brown eyes with thick eyebrow extensions and black eyeshadows. If you wanna appear to have her eyes, you should get some eye makeups, that is basic. On the other hand, try to get a pair of contact lenses with brown color. Hope you find this useful.