The most useful way to better benefit from a research trip to a library is to ask a librarian for help. They are highly qualified workers who not only know the library, but also where to find specific sections, but they also know other research tools (in and without the library) that might improve your research and provide new sources you had not heard about. Most libraries allow visitors to schedule 1:1 meetings with a librarian to discuss ways to research the topic in question or to even better define a research topic.
Almost all libraries offer online catalogs where users are able to find books, DVDs and other materials available. The online database is useful for two main reasons: it is a way to browse other related sub-topics and keywords that might be helpful to the research and it also allows guests to make book reservations prior to their visit to the library.
Libraries might seem confusing at first, with many sections and rows and more rows of bookcases, but once the visitor is familiarized with the place and with call numbers any search becomes easier. Call numbers are the numbers that each book in the library has and it indicates the book's physical location. Libraries often present maps that indicate where each group of books is on each floor. The most important hint, however, is to notice that books are always grouped together with other books of similar topic, so pay attention to the books nearby specific works you are searching, as they might be just as helpful.
In this era of technological advances, most visitors consider card catalogs obsolete search tools at libraries. Although most libraries prefer to categorize their items on digital catalogs, most of them still keep their card catalogs as another way to register all items present in the library. Sometimes, when items are antique or of restricted perusal, some libraries do not insert the information about them on their computer database. Card catalogs, then, would be (other than talking with a librarian) the way to get to know about the existence of certain interesting and useful items at the library.