I watch it just as intently as I do the action after the opening bell. I liken it to watching and studying the horses an hour before and all the way up to the start of a big race. You certainly wouldn't bet on the horse that limps up to the starting gate, nor would you bet on one that is acting erratic, that the jockey couldn't control. Those who skip the premarket action are simply walking into the racetrack just as the starting gate opens. They have not seen the whole picture and are more apt to make mistakes.
Trading is no different.
By watching the premarket action, you can see which stocks are tired, which ones are ready to leap out of the gate with a burst of momentum, and even more importantly, which direction they will most likely go. Here are examples of a few that worked and a few that didn't. On Friday, Jan. 19, and Monday, Jan. 22, I noticed that the trend was for stocks to drop at the open then bounce. Because the premarket action looked similar, I was expecting much of the same. As you can see from the Nasdaq chart above, it followed Monday's lead by dropping at the open then bouncing.