Well, having not seen the image, I'm gonna take a shot at it.

Use the Lasso Tool to select the "general" unwanted areas and Delete them.

Make a Layer Mask and paint black to hide what you don't want to see - that way you can also vary the softness/hardness of the brush depending on what is in focus and what is not.
For edges that go a long way that are smooth and rounded (think of the side of a watchface, coffee cup, hood of a car, etc.) use the Path Tool to create a spline that matches the curve, use that selection (feather .5 pixels for sharp edges, or it will be TOO sharp - otherwise feather to taste if it's soft) and paint black (or just fill) to hide/show what you do/don't want to be seen.

Hope this helps-
-Lew ;-)