Center the art, not the blur…
The one thing neglected in many of those tutorials is the fact that many Photoshop effects default to the center of the image window. There's nothing you can do about it. So, naturally they use a centered subject photo so their (easy) tutorial works perfectly every time.
So, what we've got to do is bring the art to the effect, rather than bringing the effect to the art.
The first thing you've got to do is increase the Canvas size so you can move your photo around… follow along:
First, make a copy of the art or photo. I usually just select all (cmd/A) and then "float" a copy (cmd/J). This puts a copy of the art on a new layer.
I know I'll need the original later.
Use the Crop Tool and drag the handles well beyond the edges of your image. When you commit that crop (just double-click inside the cropped area) your canvas will immediately expand to accommodate.
Since the Radial Blur uses the edges of the image to find center, we'll place our subject at the center of the newly sized canvas.
My method of finding center is the old-time photo cropping method of simply drawing an "X" through the art. Where the two lines cross will be the center. So on a new layer I grab the line tool and simply draw from corners to corners.
Now, using the Move tool (Tap "V") I move the part of my subject I want centered to where the lines cross. The young lady's face is what I want to concentrate on.
Now set the Radial BlurFilters > Blur > Radial Blurand select "Zoom" or what ever effect you like.
With your blur finished, we'll return to that original we saved earlier and paint back in some sharp detail.
Note here that I've moved the original up under the blurred versionNow click on the "Layer Mask" icon at the bottom of the Layers Palette, and then click on the mask thumbnail. (Note that the thumbnail gets a double border, indicating it's the active object.)
Using a very soft-edged brush, set to about 80% opacity, I'll begin with the face and paint black into the mask. As I paint, I can see the detail coming back into my photo.
Paint just the parts you want revealed. Here, I painted all the face and torso, then did some sketchy paint out into part of the legs and arms.
SIDEBAR: Folks, you don't have to use the mask — you could simply use the eraser tool and remove pixels to reveal the sharp image below. I use a mask because it's "non destructive" and if I goof up, I can always paint back in with white, or start again.