When you get in the ready position, you need to be ready to field a hot line drive AND ready to move. Many players forget the second part (ready to move). They crouch down with their feet very wide, their gloves almost on the ground, and their palms facing the hitter. When the ball comes, these players probably look like they're holding a skillet rather than a glove.
Just as a hitter needs to stay relaxed to be quick, the same also applies to an infielder. The ready position described above creates a couple of problems for the fielder.
The ready position is an athletic position that allows you to move quickly in any direction.
Most players devise a pre-pitch routine that puts them in the ready position as the ball crosses the plate. This may be a shuffle of the feet or a little hop. Whatever method you use, make sure you're balanced, comfortable, and ready to move. Get your momentum moving forward. Don't sit back on your heels. You want to be aggressive and play the ball rather than have the ball play you. This can only be done if you're moving forward and ready.