Some call when they have particular issues that come up. Others like an update more frequently. Astrology has a tremendous amount of information to offer. A good astrologer can provide useful new material as often as once a month. Fees vary widely depending upon the region, experience of the astrologer and type of clientele.
Sessions usually last an hour to two hours.
Make sure your consultation is taped so that you have a record of all that's been said. The best way is by word of mouth. If you know someone who's been helped by a reading ask who did it for them. You can also check sources on the Internet, through your local astrological society, metaphysical bookstore or any of several national organizations. Don't be afraid to ask questions about the astrologer's practice, training, approach, follow-up, etc.