For the last pic...did you just slap the renders on?...I mean, it has minimal/no blending...come to think of it, I can't find much blending in the other works either. I know Zophia mentioned it...but w.e. :P
Oh, and if you are using tutorials, which I see you did, don't stick to it/follow it line by line...understand what they are doing and add your own thing to it
And, when it comes to choosing renders, try get ones with more movement in it...I say this since your background has good movement.
And, I'd just like to mention, try stick away from text/type until you have mastered it...text can either completely destroy a good piece of art work, or can make it wayyy better...Typography is a whole different science...master normal sig making first