If you are looking for books on a particular topic:
Keyword Searches: Enter a variety of terms in Primo that you think describe your topic. When you call up a record that seems promising, mine its subject terms to find similar items. To do this, simply click on one of the subject headings listed in the record for the book; the next screen will list all the books in Primo that share that subject heading.
Subject Searches: Familiarize yourself with the Library of Congress Subject Headings and the call numbers associated with them. You may also consult the print version (four red volumes)--ask for them at the Information Desk. Library of Congress Subject Headings are not always predictable and may reflect previous generations' biases. Here are some sample subject headings so that you can get a feel for the wording and structure typical of Library of Congress Subject Headings.
When you find a subject heading that describes what you are looking for, you can run searches in Primo and/or go up to the stacks and browse the shelves within that call number range. Never underestimate the effectiveness of browsing!