Big subject, and there are books written on this, of course. There are a few mentioned here.

But , just working from what you've written here about people in the field publishing histories of it but not training as historians, I think that a good place to start is: what are the questions to be answered and/or who gets to pick them? R.G.Collingwood pointed out that a great deal of what's written depends on what's been asked. For example, there has been a good bit of writing about the history of technology with the people in a narrow field asking the questions. So, you could find a book that goes into great detail about the evolution of the flintlock mechanism ( when a tumbler was equipped with a fly, who made one first) that has been obviously written by and for firearms collectors, whereas someone who is not a collector might instead be asking, why did this culture think it important to modernize the gun, and why did this other culture not bother? Or, did the ivory inlays in the stock mean there was a trade with Africa? How did that work?

This is not to say that limited very technical history of flintlock mechanisms is a bad thing: it might be intended for that audience alone, and that's likely OK. But it is important to decide on the questions, not just assume they will be obvious.

EDIT There are quite a few useful research guides online. To me, they state the obvious but I have to admit that what is obvious to me may not be to someone else just starting out. This one is pretty thorough. I personally think that notes on index cards are now somewhat outdated, and replaced by software tools like Scrivener ( and a removeable backup !) , but some people are more comfortable working with paper.