What do you mean by a good conductor

How do you become an amateur conductor?

1. Your regional music association
There are various courses there. The C series should be interesting for you. There is the C3 course there. However, you have to complete the other or at least a large part of the other courses beforehand, unless you can provide any other evidence (completion of a music degree, etc.) that confirm your skills.

2. Books
There are countless books about conducting (e.g. by Felix Hauswirth, Alfred Pfortner, Henk van Lijnschooten, ...). Robert Kuckertz even has a DVD about conducting.
In addition, there is Michael Stecher's book, which I would consider "compulsory reading" for conductors. His "rehearsal pedagogy" leads to its own new pedagogical model. What use is the most beautiful technology if you only sit there with 5 musicians because you have stepped on everyone else's feet and nobody can stand you anymore.

At this point, I would like to emphasize that books can only serve as a support and that you cannot learn to conduct on the basis of books alone. You have to have an orchestra with / in front of which you can practice.
It's also funny to conduct the CD player, but it doesn't drag, is never too loud and usually quite resistant to your conducting movements (maybe your musicians in the orchestra, too, but you can change something).

To finally answer the question: one becomes a conductor by conducting. At the beginning of all conducting activities there is a technical game. If you are conducting a piece in 4/4 time and a 3/4 comes out, you mustn't think long about how it was conducted again. Depending on the performance level of the orchestra, you can sometimes be confronted with unsightly time signatures such as 11/8 etc. and you must / should always be able to conduct them cleanly and recognizable for every musician.
Then there is the left hand, which should move relatively independently of the right and should not be its reflection.
In addition, there is the pedagogy already mentioned, which should by no means be disregarded.

Maybe you ask your current conductor if he can help you a bit in learning all of these things from the ground up. After that you can look around for further training courses.