Lightroom 4 has different tools for applying local tweaks. I use the ‘Graduated Filter’ tool a lot. I like it. It can improve a picture in a subtle manner so you won’t notice it (if you do notice it, the effect is ‘overdone’). But sometimes a ‘gradient’ is not enough because you really need a more precise local tweak. Enter the ‘Adjustment Brush’ tool.
Below I have a picture of my family in New York, eating a ‘hot dog’. This is a ‘must have’ picture but unfortunately it was shot while my wife and kids where in the shadows. Difficult to improve with global tweaks. Here you can use the local ‘Adjustment Brush’ tool to your advantage. Select it, ‘paint’ the desired objects (in this case my wife and kids), and apply the desired local tweak (in this case I up the shadows, see sliders). You will notice that my family is now much better visible, but, because the tweak is not ‘overdone’, the picture in total is still correct. A pleasing result. And the ‘must have’ picture is improved for keeps;)
The final result below. ‘Hot dogs in New York’ :)