There are keyboard shortcuts for almost everything in Photoshop, including changing the opacity of a tool. To change the opacity for any tool that supports it, just press any number from 1 to 0 and the opacity will change from 10% up to 100%.
For more control over this, you can press (for example) 7 then 5 to get 75% opacity.
For more flexibility when working with rounded corners in Illustrator, you can instead of using the rounded rectangle tool, use the standard Rectangle tool and draw your base shape. After that, go to Effect > Stylize > Rounded Corners. This will be saved in the appearance panel with the bonus that you can go back and change the settings whenever you want.
When you are dragging a selection using any of the Marquee tools you can hold down the spacebar key (not letting go of with mouse) to be able to reposition the selection before committing to it.
Many Photoshop users don’t know that Photoshop has a built-in set of rulers that can help you align objects in your documents. To activate the rulers at the top and left side, use the keyboard shortcut Command + G (PC: Control + G) or by going to View > Rulers.
To drag out a guide to the canvas, click anywhere in the ruler bar, hold and drag out to the place you want on the canvas.
There are two excellent keyboard commands that you need to know about when working in Photoshop. Firstly, to quickly reset both your foreground and your background color to their defaults, hit the “D” key (D for Default).
Secondly, to switch between the foreground and background colors (make foreground the background and vice versa), just press the X key.