Lightroom Tutorial - Depth of Field Enhancements
|Figure 1: Before and After. ISO 100, 1/80 sec, F/5
|Figure 2. Baseline adjustments
|Figure 3. Adjustment Brush and Settings
As far as brush settings. make sure you have a pretty large feather setting for it. You can turn on or off Auto Mask (most times I find it in the way). I usually keep it off as it sometimes creates undesirable masked areas that don't show a nice smooth transition.
|Figure 4. Mask display modes
hitting 'O' key will toggle
Painting the area with Mask Overlay on.
Your end results might need some minor adjustments, but what you should end up with is something that brings that foreground element more in focus while subtly blurring the background further.