Creating animated shining car effect

Start by opening an image of a car.
Create a new layer. Create a white spot using brush tool with soft brush settings.
Create a selection of the edge using polygon lasso tool.

Click add layer mask button from the bottom of the layer palette.
Unlink the mask with the layer content. Select the mask thumbnail and try to move the white flash to check if it's looking fine.
Similarly create a selection of the top of the car.

Create a new layer and create a white flash and mask similarly. You can add this flash in other parts of car too.

 

Open animation window. For the first frame move all the white flashes out of the visible bounds.
Duplicate frame. Move the flash on the top of the car by moving it's masked content towards the front glass.
Click tween button from animation window. Apply settings as shown.
Similarly move the white flash on bonnet edge and other body parts. Tween the frames as mentioned above.

 

Press Ctrl+Alt+Shift+S to save an optimized animated GIF.