Focusing Images Guide
I decided to give focus to the close-up daisy in this picture:

Use the Quick Mask Mode (Q) and draw a smooth area around the flower.

Make this area a selection. Now use Filter - Blur - Lens Blur with these settings:
- Shape: Triangle
- Radius: 8
- Blade Curvature: 50
- Rotation: 0

Now use again the Quick Mask Mode (Q) to select a more detailed area than the first one.

Make this area a selection, then use Filter - Sharpen - Unsharp Mask with Amount: 75% and Radius: 1.

You're almost done. But I thought the picture looked a bit too dark, so I went for Image - Adjustment - Curves and fixed two points at [75;45] and [185;170]. Then set Image - Adjustments - Brightness/Contrast to Contrast +30.

You're done!