Cervical mucus changes throughout the menstrual cycle. During the first half of the cycle, it will be different from the cervical mucus after ovulation, and in the luteal phase it will change again. Women who have used their cervical mucus to determine whether or not they are fertile swear by this method, and say that it is extremely effective whether it is to avoid pregnancy, or to conceive sooner. There are periods of life when the cervical mucus may be a bit confused. If you have recently given birth, or are menopausal, studying cervical mucus is not an effective fertility monitoring method. In addition, the key to this method is experience. While there are plenty of online resources that give information about what your cervical mucus is likely to look like at a given point in the cycle, this does vary for every individual woman.
Therefore, getting to know your mucus and perhaps taking notes on a calendar is the best way of making sure the technique is effective. I just recently got my menstrual cycle back following the birth of my second child, and I decided to give the mucus method a go myself, out of curiosity more than anything. I have had two periods now, and based on the mucus, I think I ovulated once. I found that the structure and color of cervical mucus I noticed largely corresponded to the information that is available. I would not go by this method alone if I wanted to avoid a pregnancy, however.