The brush tool can be your best friend in Lightroom, allowing you to add just about any adjustment you like onto very specific parts of your image. But did you know LR also lets us have 2 brushes set up to quickly switch between the amount of adjustment being added?
With the A & B brushes, you can set a different Flow and Density for each, letting you choose and quickly switch between the amount of adjustment you're painting on. Sometimes you'll need a high Flow and Density to achieve a powerful effect, other times you'll want lower settings to give you much more subtle changes. Set up your A & B brushes to your most common needs, and start saving time!
And what the heck is Auto Mask? Basically, it's LR's way of coloring within the lines. If you have it turned on, and you're painting effects on areas with very definable lines, say a red car against a blue sky, LR will try to follow the lines in the image, allowing you to paint a bit faster and with a little less accuracy than you may think you need to.