If you’re tired of tapping the left and right brackets to increase / decrease your brush size, try using the drag-resize brush cursor keyboard shortcut in Photoshop to make rapid changes to the brush size. Ctrl + Option (Mac) / alt + right click (Win) -drag left to right to decrease/increase brush diameter while displaying a red overlay of the density and feather of the brush for visual reference. Drag up and down (using the same shortcut) to increase/decrease the hardness/softness of the brush. If you prefer to change the Brush Opacity (instead of the Brush Hardness), based on the vertical drag movement, select Preferences > General and uncheck “Vary Round Brush Hardness based on HUD vertical movement”. By disabling this preference, Photoshop enables a change in Opacity when dragging up/down.
To customize the display of the Brush (as well as other cursors), select Preferences > Cursors. Select one of the following: Standard (the small iconic cursors), Precise (cross hairs), Normal Brush Tip (size represents pixels to be painted with greater than 50% effect), Full Size Brush Tip (size represents all pixels to be painted). Check “Show Cross hairs in Brush Tip” to easily see the center of the brush. To display only the cross hairs in the brush enable Show Only Crosshair While Painting.
Other Tool icons can also be set to Precise in the Preferences > Cursors dialog, or can be temporarily invoked by enabling the “caps lock” key.
Finally, the red color overlay can be customized in Preferences > Cursors > Brush Preview.