Erase the background, or at least make it a lot less detailed than your foreground. Tone down and alter the detail in places where it wouldn't be as plausible. For example, your shirt looks like it was shaded by dotting the paper; line-based shading would be more realistic for a pencil drawing. It might help you to draw a simple sketch of this on paper (doesn't have to be accurate or even good, but at least try), just to have a reference at hand for what certain things look like when done with pencil (i.e. shading, line thickness). You can use that to get a sense of details and tweak your image accordingly.