A major component to beginners golf that I never realized is that you must keep your left arm straight. This was pointed out to me by my friend who was watching my back swing. Look at the pros, the left arm in the back swing is straight. If you take your left arm, point it straight away from your body, take your right arm and grab your left shoulder, pull left arm to the right. This motion is crucial to the golf swing because it helps build compression in the back swing and maintain a steady follow through.
This is not a tip I learned through Google, however hitting up youtube and following the instructions in these videos will emphasize my point.
Left arm straight at the start, through, and at the finish of the swing - http://youtu.be/Lo_HvZxTBSE
The below video is ideal for people who cannot obtain full rotation with a straight left arm. If you have a thicker upper body or a heavy middle section that makes it difficult to get a full rotation, which is bringing your left shoulder to the point where the ball is, then look at the below video.
Left arm straight at the point of impact - http://youtu.be/4Lw9eYpZyrs