When I first began writing, all research I did was at the library. I looked at microfiche or checked out books. I took copious notes, which I kept organized in binders by subject. I also copied pages from books and kept those with my notes.
Now, I also use the internet. But even with the internet, the most reliable sources are still books. So I still use them. I'm sure you do, too. And like always, keeping track of this research is challenging. Keeping it organized is necessary.
You have several options for organizing your research. One is to keep the hard copies of everything—your handwritten notes, pages you copy, or articles you remove from magazines. These should be kept in a binder or file box, depending on the size of the project.
Another option is to scan in all your notes and keep them on your computer. You can discard your hard copies, which reduces the amount of paperwork in your office.
Or, you can do a combination of the two. Keep some notes in hard copy, and scan pages from books. Only you know what you are comfortable with.
Let's look at hard copies first. You'll need a binder or file box to house the notes for the current project. Within the binder, insert dividers for each subject. For an historical, these might be fashion, transportation, society, architecture, etc. For a thriller, these might be weapons, self-defense, or police procedure.
Whenever you take notes or copy anything, make a notation of the source on the pages. You may need to find it again in the future, or prove your source to an editor. To save yourself time, create a master list of your sources. Assign each source a number, then write that number on the pages instead of the title, author, call number, etc. Also keep track of where you found your sources (library, friend, etc.) in case you need to borrow it again.
When done with a page, place it behind the corresponding divider. You can further divide within each subject. For example, fashion can be subdivided into Men, Women and Children. Whatever your needs, keep adding in sections. There will be some similarities between books. Others will be specific to your project.
If you scan any of your notes, keep the subject files in your computer corresponding to the subject headings in your binder. Consistency is key.
As you write, and find you need to do some fact-finding, you'll be able to find what you need in just a few seconds.
So how much of your research is still done in the library, and how much online?