Shift + F clears all text and HUD from the screen.
Shift + U activates user cam so you can set up your shot nicely. Try to get the sun shining on the facing view. Spacebar hides/unhides the controls.
Print Screen on your keyboard copies the image to your PC's clipboard.
Shift + F4 minimises LFS to a window.
Open your graphics program and create a new image the same size as your screen resolution, 1024 x 768 for example.
CTRL + V (paste) pastes the clipboard contents into the new document.
*To get rid of those yucky jagged lines make sure you have Anti Aliasing set on at least 2X in your graphics card's advanced properties before taking the screenshot.