At first, you may find it easier to clean your baby's teeth using a piece of clean gauze or muslin. Wrap it around your finger, put a tiny smear of toothpaste on it, and rub it around your baby's teeth.
If you'd rather use a baby toothbrush, pick one with soft nylon bristles and a small head. This will allow you to reach all parts of your baby's mouth easily and comfortably as each new tooth emerges. Look at the packaging to see what age range the brush is designed for. Also remember to replace your baby's toothbrush regularly, about every one month to three months. If the bristles start to spread out, it's a sign that the toothbrush needs changing.