My twin has very twitchy eyes and I have to help him apply eyeliner because of that. What I do is that I hold down his eyelids by the lashes and then just draw. It works well and I do the same when I apply eyeliner on myself.
*~Cosplays in progress~*
Masamune Date - Sengoku Basara
Eren Yeager (casual outfit) - Attack on Titan
Sanosuke Harada - Hakuōki: Shinsengumi Kitan