Monthly horoscopes: what they can do
Monthly horoscopes by sun sign are the most widespread astrological format after the daily paper. It is worth knowing what they can technically deliver in the first place.
What they rest on
At best: the transits of the slower planets through the sign concerned, and the lunations of the month. That is a real basis — transits are a recognised technique.
At worst, nothing at all but routine.
Why it still says little
Because a transit to a sign is a different matter from a transit to a chart.
A transit takes effect when it touches a point in the birth chart — a planet, an angle. Which point that is, and whether one is touched at all, depends on the individual chart. For a twelfth of the population at once, that cannot be said.
On top of that, without the ascendant there is no way to tell which house the transit falls into — that is, which area of life. And that would be precisely the interesting piece of information.
What would yield something in its place
The profection: the ascendant moves on by one sign for every year of life, the ruler of that sign becomes lord of the year, and the monthly profection divides the year up further. It is individual, it can be dated, and it needs a time of birth.
Alongside it the solar return and the primary directions — and the rule that only what several techniques show in agreement is reported. See the quality of a stretch of time.
A fair conclusion
Monthly horoscopes are entertainment, and as entertainment they are fine. They become a problem only when they create fear or advise decisions — the basis for that is too thin, and demonstrably so, not as a matter of opinion.
See also: the yearly horoscope, why a reading feels accurate.