*EDIT* Julia from JiuJiuBJJ recommended that I clarify this one a little bit to make it more clear what I'm talking about. So here we go!
*EDIT 2* The lower res video was annoying me. So I uploaded the original HD cut. The black box STILL annoys me. Gotta figure out WTF my camera/editing software is doing...
This video is of me rolling with one of our whitebelts. In it he makes several mistakes which are common to white belts. I'm going to discuss a few of them with a primary emphasis on what happens when you over reach during your passing attempts.
At the beginning you can see where I establish my grips and insert a DLR hook. I then strip his grips and while I'm slapping his hands away I barely shift my hips and transition to his back. I roll through to mount, then back to his back and continue to control him, then move to the armbar for the finish.
Minimum effort for maximum results is the name of the game. He pushes forward, but doesn't know how to get past my hooks, so I'm able to control the game from there. He never is able to get ahead of me during the transitions so he never really has a chance to avoid my attack.
His biggest mistake, and what allowed me to sweep him is his continued attempt to attack my collar to the exclusion of everything else. Even after I have established hooks he continues to ignore my legs and grasp at my collar.
What he should have done is to stop grabbing at my collar and grab my pants instead. Allowing me the use of my legs makes it infinitely more difficult to pass my guard. It's commong for white belts to attack as far forward as they can reach and leave half of their opponents weapons available.
Instead you should begin by controlling the ankles and work inwards in order to immobilize your opponents weapons in the most effective way. Controlling the ankles, then the knees until you are past the hips, then pinning the hips and beginning to isolate and attack the arms while working to disrupt your opponents posture to prevent them from escaping.
Don't be over eager to attack the neck. Ignoring your opponents legs is a huge mistake.