Go See a Peer Advisor

Many departments have peer advisors, students currently in the major who are trained to answer questions about classes, declaring, opportunities within the major, and all sorts of other relevant topics. They will usually have open drop-in hours, and you can bring very informal questions, or specific questions about logistics such as finding an advisor, or picking classes. Reading the peer advisor bios can also give you a sense of the pathways within the major.
It’s Never Too Early to Visit a Peer Advisor
They are a great starting point if you are considering a major, even your very first quarter here. You can simply ask “why did you decide on this major? What should I know about it? What classes do you recommend? How did you decide among tracks? How do I get started with research?" and so forth. No preparation needed.
How Do You Find a Peer Advisor?
Not all departments have them, but if they exist, you should be able to find the information on the department website. Try searching “peer advisor [name of department]” from the Stanford home page, or other keywords as noted below.
Here are a few selected links. Heads-up: the list below is not exhaustive! Even if you don't see a department listed here, check to see whether they may have peer advisors, or student mentors, or a similar group.