This is a typical beginner mistake, the canvas size is a bit too big and as a result there is a lot of space which you had to fill.You did a gret job at the blending of the render, but the render ain't the focal point anymore. When you look at the sig without focussing on Sasuke, my attention goes towards the effects. I don't know if you are familiar with the concept of flow, but this is may be a great signature to explain what it is.
Flow is essentially the direction which your attention goes to when looking at something. Before I continue the CnC, I ask you to look at your own signature without paying any attention to any part in particular and tell me where your attention is going to (so youhave to forget that this signature is all about Sasuke).