Try adding a vignette
First, choose the Elliptical Marquee tool (left-click and hold on the Marquee tool to see this option). Drag a circle around your subject, right-click and select Refine Edge. Set Feather to 300 pixels and click OK. Use Shift+Cmd/Ctrl+I to invert the selection, pick the Paint Bucket tool (G) with black as the foreground colour (D) and click in the selection. Reduce the layer opacity to 30%.