How do you look for classic/normative/standard books about an established branch of mathematics?

Question

If you want to immerse yourself in a branch of mathematics (e.g. linear algebra and linear optimisation) which is new to you, then you often look for standard books which you can rely on. You could call them classic, normative, established, popular, widely-accepted, etc. Typically, such work is referred to in introductory courses. If you are lucky, you are attending a relevant course (e.g. at university) held by a lecturer who could enumerate advisable literature. Otherwise, how can you quickly find/identify the literature to start out with - e.g. the 1-3 most standard textbooks of the branch - without already being an expert?