Dick Light gives a pretty decent talk during freshman week... the two big takeaways I had were:
1. Whether college sucks or rocks depends on how well you manage your time.
2. Make friends with at least one professor each semester.
Try a bunch of different activities freshman year - both stuff that you've done before + things that are completely new. There's no need to narrow things down immediately (but I would recommend doing it eventually, being an officer of an organization is incredibly rewarding).
You may want to think about a smaller concentration - More discussion about that here:
"Low Ranks for Large Fields"
Make the most of your summers -- talk to upperclassmen about what they've done, what they wish they had done (my advice - go abroad after your freshman year!). And more broadly, get to know some upperclassmen (through ECs is the easiest way). They can help you find good classes, fun parties, etc.
Get to know a bajillion people during the first few months. There's only a short period of time where you can sit down at a table in Annenberg with a group of people you don't know, and it won't be awkward.