How you open the clay on the potter's wheel will effect the rest of the throwing process. If rushed or done with poor hand placement, the pot may be doomed to be off-center.
During opening and creating the floor of the pot, the wheel should be rotating at either full or three-quarter speed. Keep the clay's surface well lubricated. It can be advantageous to keep a sponge tucked into your right palm so you can release water onto the clay as needed, without having to cup water and bring it across from your bucket.
Your movements should be firm and smooth during opening and throughout the throwing process. It can help to keep your movements at a fairly slow pace, especially when first learning. Quick pushes and releases on the clay can result in the clay being knocked off-center.
Opening the clay must be done so the opening is centered. To find the center of the clay, lay the fingers of your right hand across the top of the centered clay so that they go over the mid-point. Rest the tips of your left-hand fingers on the backs of your right-hand fingers. Positioning your hands in this way will ensure that the clay will open on-center.