Screenshots: Press the PrintScreen key on your keyboard to make a screenshot. Create a new document and you'll notice that it's automatically set to the resolution of your screen. Go to edit/paste or press Ctrl+V to paste the screenshot.

Press ALT+PrintScreen to make a copy of the active window only. Be aware; sometimes Windows will copy the complete screen when you think you've selected only a single window. A good example is the layers palette. In case you want to make a screenshot of the layers palette only; make sure that you click on one of the tabs first, otherwise you might end up with a full screenshot instead of a one of the layers palette only. Save screenshots of menus in GIF 32 colors to save bandwidth, unless you have an image that contains a document window with pixel data.

Select the area that you want to mark with one of the selection tools. Now go to edit/stroke, select a width of 2, color red (or any other color, I prefer red) and click OK.If you want to add arrows; go to the Line Tool (U)
Select arrowheads by clicking on A (see screenshot)

I prefer a weight of 2 pixels.

There are situations that you want to sample a color that is outside your document window or even outside Photoshop. Select the Eyedropper Tool (I) and click inside the document window but hold down the mouse button. The move your eye dropper tool to any area of your screen and release the mouse button when you want to sample a particlar color. Of course you have to make sure that the object which color you want to sample is visible before you start sampling.

You can quicky switch between burn and dodge tool by holding down the Alt key (or option key on the Mac). It doesn't matter which of the two, dodge or burn tool, is active.

• Open Picture
• Double click on background layer
• Select Rounded Rectangle Tool (U) (Make sure that Paths is active)
  
  
  
• Adjust radius
• Make the rounded rectangle
• Select Layer/Add Vector Mask/Current Path
• Create a new layer beneath this layer

You can use the crop tool and enter a width and height in the option bar, but when you click on the crop tool and make a selection you'll notice that you can resize the selection. As a result of this the actual crop will resize to image data that is inside to selection to make it fit the predefined values for width and height. This is not always what we want. To make use of a predefined crop without resizing:

• Create a rough rectangular selection using the rectangular marquee tool
• Go to Select/Transform Selection
• Resize or move the selection or enter a value for height and width.
• Note: the values for height and width are shown in percentages and to enter a value in pixels you need to type in a number and end it with the letters px.
• Use ALT + middle mouse button (if you have one) to zoom in/out and use horizontal or vertical scrollbar if you want to change the view (of course you can also use the Navigator Palette)
• Select Image/Crop and Photoshop will use the selection to define the size of the crop without resizing the image

For those who didn't know this; if you want to get rid of all image data outside the canvas:
Select the complete image: Ctrl+A (Command+A on the Mac)
Select Image/Crop

This is an image that needs strong saturation:

In this example I've (over) saturated the image with a saturation setting of +68.
You'll notice the appearance of noise and jpeg artifacts:

This is a way to avoid this:

• Duplicate image to a new layer and make this layer the active layer
• Saturate this layer with a saturation of +68
• Go to Filter/Noise/Median... and select 4 for radius and click OK
• Go to Filter/Blur/Gaussian Blur... and select for radius 1.6 and click OK
• Switch the layer's blending mode to color (default is 'normal')
  

Assume that you have a layer mask and you want to copy it to a different layer. Activate the layer that you want the layer mask to copy to, then click on the layer mask of the layer with the mask, hold down the mouse button and release the mouse button when the cursor is on top of Add Layer Mask icon

This will copy the mask. If you want to copy an inverted copy of the mask, then hold down the Alt key (option key on the Mac) before you drag the mask.

Select the Layer Set and while holding down the Alt + Ctrl key (Command + Option key on the Mac) click on the Delete Layer icon in the layers palette.

When you resize an image that contains layer styles you have to select the Scale Styles option in the resize in the Image Size Window (Image /Image Size...):