hmm, make sure your whole tagg is one piece. it has to flow, it has to look natural; as if the render was supposed to be in that area.
I like the grungy bit on the naruto one, but it doesn't fit the render's style. just keep that in mind. good examples are tutorials: if you see a tutorial of a good tagg (deviantart.com) you will notice the background is build around the render/focal