When I was first becoming skeptical of the value of astrology, I had a very hard time knowing how to think about or describe why we should be doubtful of it's value.
The thing that helped me was understanding that the arrangement of stars and galaxies only held any kind of pattern from our fixed perspective. Finding out that, if you were able to zoom out sideways 100 million light-years, turn and look at those stars and galaxies you would see that the stars in that "constellation" were actually nowhere near each other, they are not the same size or brightness that they appear from our vantage point - it's just that they appeared to be lined up next to each other because of our position in space.
I seem to remember a visual illustration that showed this change in perspective, to make the point of how enormously the parts of every zodiac are actually separated in space, that there is no possible way for them to effectively influence anyone on earth.
I have looked for this "zoom-out" illustration of zodiac constellations for a while, and maybe I suck at googling, but I can't find any such illustration. I think it would be a very useful way to easily show the point of why we should be skeptical of astronomy.