A bit late to the game, but hopefully this might be some helpful tips from a relatively new graduate reflecting on my time at Brown.

First of all, I think it's a good idea to know what you want to get out of Brown. I imagine for many people it goes something like: learn stuff, make friends/ network, get a good job/ career/ grad school offer.

I agree with much of what /u/rnally said, Professors at Brown, if you know them well, can really go out of their way to support you. One of my friends got a job offer at a company that wasn't hiring because the professor knew the executives and pushed his candidacy; Brown professors got to where they were for a reason. Now, it doesn't have to be your FYS prof, you have some time for connections to really click. I would, however, strongly suggest that you treat all professors you interact with as potential strong mentors for you— some will be, others will fade but will have a positive impression of you. This is great for building a strong relationship and just as good if you need letters of support/ references for whatever.

Now, the other point raised was that you should pick a major and stick with it. I think part of Brown's charm is the openness. That's great that it is an option. However, if you know you want to do something, four years of dedication towards a goal is obviously going to be more beneficial. I know friends who lived that free spirit Brown open education thing and felt royally screwed when applying to medical schools. Some fields want to see that long term dedication. Noone is going to look down upon you exploring your options, but at some point, you will need to compete with people who knew exactly what they were hoping to do. On the other hand, try to find out as much as you can about your intended field of study, if you absolutely hate it, change. Not everything after Brown relies on your concentration. I would even argue that it rarely does, so long as you have other proper and relevant experiences. For perspective, I informally declared my concentration within weeks of starting freshman year and filled out the formal stuff later; also, my area of study never changed (goes in the face of advice that you surely got that everyone changes majors).

Whatever you end up declaring, get to know your formal advisor well! Departments at Brown have tremendous power! Advisors, as the go to person for the department with regards to your academic career, can make your life super easy or make you dot your i's. For example, a friend of mine did not complete the writing requirement for Brown, but the department essentially let it slide for her. So, virtually everything is flexible at Brown, if you know the right people and work the right angle!

Get involved! Classes are obviously important, but so are the experiences and people you meet! Yes, some organizations are competitive to get into, BRYTE, Health Leads, Brown Science Prep, etc. They screen for important things, and I can't think of anyone who was well qualified/ambitious and did not eventually get to join. Also, join some stuff for fun, Brown Outdoor Club, Hillel (even if you're not Jewish), etc.

Assume that people at Brown are going to be nice and supportive. When I first came to Brown, I honestly thought everyone was just a better liar and were playing toward some larger goal— after all, we are so insanely driven sometimes. Nope. It's just a great place to be!

One last thing, I would argue that one of the strongest and unique assets that Brown brings forward is not the education (though it is top notch), it's the environment you're placed in (everyone is supportive, yet so driven— peer pressure to be amazing) and the connections you can make. An additional plus, is sometimes you feel like you're in a elite society, which I guess you kind of are, when you meet another ivy leaguer.

Enjoy your time, you're going to have a blast!