It's funny that I should see this thread today because I've just spent the past few days figuring out how to make my icon appealing and eye-catching. I hope I can offer some insight to my thought process and receive some suggestions.
This is my first take on my icon. I liked it as an individual piece, but I wasn't sure if it stood enough, and I didn't think it conveyed the tone of my story. It looks more light-hearted and fantastical rather than the slightly more action-packed, richer, and psychological tone I was going for. From here, I painted over the icon into this:
Although I liked the lighter one better, I thought this one popped more with the contrasting colors, and portrayed the tone better with the harsh colors and darkened, averted eyes.
So I made some in-betweens of these two icons and put them to the test. I screenshotted a page of popular/trending comics and photoshopped my icons over existing ones.
I avoided putting any of mine in the middle because I think that's where the eye naturally goes. After looking at this, I thought that the red background made icon #2 too busy and the face was too dark and unreadable from a glance, and that I quite liked how the faded yellow of #1 looked amongst the others. For now, I think I prefer either the uppermost or lowermost icon in this test picture. Of course, all of this would change depending on which stories show up around yours. Maybe I went a little far by doing this, but what minimal training in graphic design I had was itching at me.
Some feedback would be nice, although I may redesign the icon entirely again to better match my story (which is unpublished and will probably stay that way for a few months at least as I work on it).