Some useful screenshotting tips, we need images! :D
First, download FRAPS (my personal choice as it's useful for a number of tasks, but any screen capture software should work.) Configure it as you wish, you'll want to hide the overlay though (there's a clear option for this). I'd recommend saving images in .png format, for the purposes of the wiki.
Second, you'll need an image editor, again there's lots of options but my personal choice for this is IrfanView as it has lots of features and is free. You'll want to crop out (Ctrl+Y in IrfanView) any HUD elements or on-screen prompts (such as the prompt to move around cover) or so on as you see fit; be sure to disable your aiming reticule in the game's options before screenshotting, simple thing but even I forget sometimes. It's also good practice to crop unnecessary portions ("void space") on each side of the image, such as on bust shots of characters. The idea is to get an image that is crisp, clear, and concise as possible.
From here you can save and rename the image so that it can be easily searched and upload it; before I do this, I usually resize/resample the image down to a standard resolution (the smaller the actual file is, the faster it will load on the page), and in some cases "Auto Adjust Colors" from IrfanView's Image menu to enhance the color of the image. When you do finally save the image, a good rule of thumb is to be short but descriptive enough that your image can be found for use on other articles.
Hope this is useful!