Let's just say that if you want to easily watch videos on YouTube, these are great shortcut tips.
Full screen view of videos: Press F11 to view the running video in full screen mode.
Play or pause a video: Pressing space bar will pause the currently running video and pressing space bar again will release (play) the video.
Volume up/ down: If you want to turn volume up or down when a video is playing, press up arrow to increase volume or down key to decrease volume of the videos.
Forward or Rewind a video: Pressing left key rewinds video 10% and right key forwards video 10%.
Skip through the video: If you do not like the starting of a video and want to skip the starting part or even want to jump over to half of the video, you can do so using keys 0 to 10. 0 being a shortcut to jump at the beginning of the video.
Lots of thanks from Parkblogger.com