Three different readings get offered and they answer three different questions. Booking the wrong one is the commonest way people come away from astrology feeling it didn't tell them anything — they asked a timing question and received a personality description, or the reverse.
Natal chart — what am I like
The chart of the sky at your birth, read as describing temperament, disposition and recurring patterns.
Book this if your question is about you rather than about now. How you handle relationships. Why a particular kind of situation is consistently hard. What you're oriented toward. It's also the usual starting point, because the other readings are read against it.
Needs your date, place and as exact a birth time as you can find.
Transit — what is going on with this period
Current planetary positions read against your natal chart, interpreted as describing a stretch of time.
Book this if the question is about a period rather than about you. You're in a transition, or just before one, or something has shifted and you want a frame for it. People most often come for this during a difficult run.
The Saturn return is the best-known example, usually discussed around ages twenty-nine to thirty.
Past life — where does this pattern come from
Themes read as carried over from before this life. Practitioners differ considerably in method and in whether they present it literally or symbolically.
Book this if you have a pattern that doesn't trace to anything in your own history — a fear with no origin, a dynamic that repeats across unrelated people, a pull toward something you can't account for.
Ask the practitioner how they work before booking, since this is the least standardised of the three.
If you've never had a reading
Start with the natal chart. It's the foundation the others are interpreted against, and it's the one where you'll be able to tell most clearly whether this is useful to you — because you can check the description against yourself.
Come with a question
The single thing that most improves a reading, whichever you choose.
A reading aimed at something specific — a decision, a pattern, a period — is a different hour from a general description. Practitioners can work either way, and almost all of them do better work with a question.
What none of them do
Predict events. Diagnose anything. Substitute for therapy, medical advice, legal advice or financial advice.
Astrology has no demonstrated predictive mechanism, and the evidence doesn't support it as causal. What a reading offers is a structured framework for reflection and an hour of close attention on your own situation. That's the thing being bought, and plenty of people find it worth buying.
Choosing a practitioner
Ask what training they have, how they work, what they need from you, and what happens if you bring something they can't address.
Be wary of predictions, of pressure toward further sessions, and of anyone who tells you what will happen rather than what might be worth thinking about.