The first general rule is that you should try to read everything that you can find on the subject. Go to the local library, get all of the books on the subject, sit down on a table and start reading through them.
After you read the few books that you have access on galleons, start reading books that may talk about them. Get history books, look at the index and just read the pages talking about Galleons.
This will widen your research. Latin American histories, Spanish histories, and English histories suddenly become a source for you.
Also look for naval histories and military history books. They all should talk about something on galleons, and you will put together an interesting picture of how they worked little by little this way.
You may want to keep track of what information you got from where. You will be thankful for doing that when you want to quote some information that you have but can't remember where you found it. There is an excellent article on how to use free software in past issues of our magazine in a series called "The amateur Historian" read that
With time, you will develop an instant knack for identifying good sources from bad sources.
Until that is the case, here are some guidelines:
* Look for a consensus over different authors. While reading different books, look for the ideas that are similar on all of them. Over time agreement on topics seems to point out correct ideas.
* Beware of fanciful accounts. If some story sounds too wild, be careful with that source. It may have been written by a crackpot. So run away of any accounts that attribute cultural achievements to people from other continents, aliens, etc.
Also, beware anyone dogmatically talking about any subject. There is a great chance that they are wrong just by failing to qualify correctly what they are talking about.
Finally, once you have something on this topic, publish an article on our magazine. Writing out the research will is fun and it feels good to share.