Taking Screenshots

Guidelines

Set the language to English, unless it's a localized screenshot.
Save as a PNG image.
Preferably, use the default settings (icons, color scheme, style, window decoration, application settings etc.).
Preferably, use compositing (Desktop Effects module in System Settings), but don't worry if your graphics card does not support compositing.
Preferably, use font "Liberation Sans" at 9pt.
If the screenshot shows parts of the desktop, preferably use the default background of plasma. Include a margin (around 20 pixels) if possible, to ensure that window shadows don't look cropped.

In this example KSnapshot is used, but other screen capture applications work as well.

Start KSnapshot
Choose a Capture mode (1)
Current Screen

Everything on the screen is captured, usually used for desktop screenshots. (Use Full Screen mode to capture all screens in a multiscreen environment.)

Window Under Cursor

The content of an applications or dialog window is captured. usually used for application screenshots. Preferably, check the Include window decorations option (2).

Region

Only a region to be defined later is captured.
Click on New Snapshot (3).
Full Screen

Current Screen

Window Under Cursor

Click anywhere on the screen to take the snapshot.

Region
1. Use the mouse to draw a rectangle around the region to be captured (for example around a window).
2. Strike the Enter key or click on Enter or double click in the region to take the snapshot.
Click on Save As... (4).
Browse to the location you want to save the image, give it a name (name.png) and click on Save

The Snapshot delay option (5) makes KSnapshot wait a given amount of time (given in seconds) before taking the snapshot. This can be useful in many situations, for example when taking screenshots of drop-down menus
It's often useful to create a separate user for taking screenshots to ensure a standard look with the default settings. An alternative is to create an Activity with the settings required for screenshots.
Use Type: Color in the wallpaper settings to get a white background.