Photoshop :: Realistic/image

I've been playing around with photoshop quite a bit these days and I can now make some image that I find really nice... But actually, I'd like to make my images more "Realistic" since they always looks like some drawn stuff.

To be more specific, I'd like to make the images I draw look more realist. For exemple, I draw some sunglasses yesterday, they were nice, but they had a pretty drawn look. Or another exemple, I tried to make a kind of game menu with a screen on the right side and the different parts on the left side, just as if it was a true game menu. To get it a little bit realist, I had to take a metalic wall already made and use it... Also, the effects were not really good looking IMO.

So actually, I don't have a good idea concerning where should I start for this "Realistic path". I searched some tutorials on the web, but the results were not really what I can call "Good tutorials", lack of explanation is a curse.