Hey there, Its been forever since I used Deviant art but I randomly found myself here today so im happy to give you any advice!
If im having trouble with a flat looking artwork I grab any pictures I have saved where I like the lighting or the colour scheme and blur the crap out of it, then throw it on top of the artwork and play around with layer blending modes. It can really give you a lot more colour and contrast depth that you wouldnt have originally thought of.
Same with textures, I love taking photos of textures so I can throw that bitch on overlay and you have instant details that you can paint over or just to give you fresh inspiration.
And with Layer styles you can just keep painting in light, with lets say a Screen layer for ambient light around the eye, and definaly Overlay layers of light around the eyeball to really brighten it up, and a dark purple Multiply layer to darken spots. And with that eye I overlayed a dungeon picture that I had done previously which gives it a more reflective look.
Annnyway, hopefully something in that info is helpful, good luck!!